Partial pre-mix flare burner and method

ABSTRACT

A flare burner that is particularly suitable for use in connection with ground flares and other types of flares in which it is important to control the height of the flame envelope created by the burner is provided. The flare burner includes a pre-mix zone including a pre-mix chamber into which air is entrained. A uniform mixture of fuel and air is formed in the pre-mix zone and caused to exit an air/fuel outlet in the top of the pre-mix chamber. In one embodiment, the amount of air in the fuel/air mixture that exits the air/fuel outlet is in excess of the stoichiometric amount of air required to support combustion of the fuel in the mixture. Fuel is injected around the perimeter of the air/fuel outlet, combustion is initiated and a flame envelope is created. By injecting a mixture of fuel and air that includes excess air into the center of the flame envelope, combustion of the central portion of the flame envelope is accelerated which allows more fuel to be flared with a given flame envelope height. The invention also includes a ground flare and a method of flaring fuel with a flare burner.

BACKGROUND OF THE INVENTION

The present invention relates to flare apparatus and methods of flaringflammable waste gases and diverted fuel stock. In one embodiment, theinvention relates to ground flare burners, ground flares and associatedmethods.

Flare apparatus and methods are utilized to burn and dispose flammablewaste gases and diverted fuel stock in a variety of applications. Forexample, flares are typically located at production facilities,refineries, processing plants and the like for disposing of flammablewaste gases that are dumped and/or fuel stock streams that are divertedduring venting, shut-downs, upsets or emergencies. The flaring offlammable waste gases and diverted fuel stock (hereinafter referred toas “fuel”) without producing smoke is usually desirable or evenmandatory. Smokeless flaring is accomplished by assuring thatnon-oxidized soot does not form in a sufficient quantity to leave theflame. This is accomplished by assuring that a sufficient amount ofoxygen is mixed with the fuel to prevent a situation in which themixture becomes too fuel rich to be effective.

In many applications, the length of the flame envelope created by theflare is also important. Examples of types of flares in which arelatively short flame envelope is desirable include aesthetic flaressuch as pit-type enclosed flares, ground flares and high pressure flareson floating production facilities. In such flares, it is often necessaryto prevent the flames from being visible to the surrounding community.On the other hand, such flares need to have the capacity to combust alarge volume of fuel at any given time. The length of the flame envelopetends to increase as the volume of fuel being flared increases.

Ground flares, also referred to as multi-point flares, are typicallyused in applications in which the amount of fuel to be flared at a giventime can vary from a relatively small volume to a very high volume (forexample, 1,000,000 pounds per hour or higher). In order to accommodatethe variance in fuel volume and allow the fuel to be combusted in asmokeless manner, multiple stages of burners are utilized. The flow toeach stage of burners is directed by a control system that is responsiveto the pressure and volume of fuel to be flared. In this way, sufficientpressure is available to each burner in operation to assure that anappropriate amount of air is entrained and that sufficient mixing of theair and fuel occurs to ensure smokeless combustion in the range ofapplication.

A ground flare system is typically spread out over a large area, forexample, three acres, and surrounded by a large fence or otherenclosure. The enclosure functions to exclude personnel and animals fromthe flame area and minimize radiation, visibility and noise to thesurrounding area. The enclosure is typically made of metal or some otherheat refracting material and is from 20 to 60 feet high. As a result,the enclosure can be costly to erect and maintain.

The spacing of the burners and flow rate of fuel in a ground flaresystem is also important. The burners need to be close enough to oneanother for cross-lighting to occur and packed close enough in generalto reduce the overall size of the system and the surrounding enclosure.For cost reasons, a minimal number of ignition pilots are desirable.Typical units include a single pilot at the end of each row of burners.On the other hand, the burners must not be so close to one another as torestrict air flow and hinder smokeless burning or cause the flames tocoalesce into a ball of fire that exceeds the height of the enclosure.Also, the flow rate of the fuel must be controlled so that the height ofthe individual flames does not exceed the height of the enclosure.

One type of ground flare burner utilized heretofore includes a pluralityof diffusion jets to distribute the fuel and draw in the air requiredfor combustion. The jets are injected into the atmosphere at asufficient velocity to draw combustion air into the jets. Upon ignitionof the fuel, air from the surrounding environment is laterally entrainedfrom above the discharge point of the fuel. As the velocity of thestream diminishes, the buoyancy effect of the hot gases then contributesto the overall mixing regimen of the fuel and air which allowscombustion of the remaining fuel to be completed.

The overall flame envelope created by utilizing only diffusion jets todistribute the fuel and laterally entrain the air required forcombustion includes a dense, central core of fuel. This central core offuel remains intact until the outer portions of the flame envelope beginto burn off. As the outer portions of the flame envelope combust, aircan then enter the inner confines of the flame envelope to complete theoxidation process. Unfortunately, due to the interaction of theindividual fuel jets, the dense core of fuel formed at the center of theflame envelope makes it difficult to increase the flow rate of the fuelto support a larger capacity without causing the length of the flameenvelope to increase and/or smoke to occur. An increase in the length ofthe flame envelope often requires the enclosure surrounding the groundflare to be higher which can significantly increase the cost of theenclosure.

By the present invention, a flare burner is provided which is useful inassociation with ground flares, high pressure flares and other types offlares. For example, the inventive flare burner overcomes the problemsassociated with the ground flare burners utilized heretofore. Theinvention also provides a ground flare apparatus and a method of burningfuel in a flare burner.

SUMMARY OF THE INVENTION

In accordance with the invention, a flare burner is provided that iscapable of combusting a high volume of fuel with a relatively shortflame envelope. The decrease in the length of the flame envelope leadsto many advantages. For example, the height of the surrounding enclosureof a ground flare can be decreased or the volume of the fuel that can beflared with an existing enclosure height can be increased.

The inventive flare burner comprises a pre-mix zone including a pre-mixchamber, a supplemental fuel inlet for injecting fuel into the pre-mixzone, and a main fuel outlet. Preferably, the inventive flare burnerfurther comprises a fuel feed conduit in fluid communication with thesupplemental fuel inlet and the main fuel outlet.

The pre-mix chamber includes a top, a bottom and a sidewall connectingthe top to the bottom. The sidewall includes an interior surface and anexterior surface. An air inlet is disposed in one of the bottom and thesidewall, and an air/fuel outlet is disposed in the top.

The supplemental fuel inlet is located in a position with respect to thepre-mix zone such that the injection of fuel from the supplemental fuelinlet into the pre-mix zone entrains air into the pre-mix zone whereby amixture of fuel and air is formed in the pre-mix zone and caused to exitthe air/fuel outlet of the pre-mix chamber.

The main fuel outlet is located in a position with respect to the top ofthe pre-mix chamber such that fuel can be injected from the main fueloutlet around the perimeter of the air/fuel outlet of the pre-mixchamber. In one embodiment, the main fuel outlet is spaced outwardlyfrom the pre-mix chamber to provide a space between the exterior surfaceof the sidewall of the pre-mix chamber and the main fuel outlet. Asdiscussed further below, this space allows fresh air to be entrainedfrom below the burner to a point adjacent to the fuel ports disposed onan inner portion of the main fuel outlet. The enhanced mixing created bysuch entrainment can be important in certain applications, such as whenheavy hydrocarbons or unsaturated fuels are being flared.

The fuel feed conduit conducts fuel to the supplemental fuel gas inletand the main fuel gas outlet. The fuel can be supplied to thesupplemental fuel inlet and the main fuel outlet at the same pressure ordifferent pressures depending on the application.

The inventive flare burner can further comprise a fuel membrane disposedaround the outside perimeter of the pre-mix chamber. The fuel membraneincludes a fuel inlet and is in fluid communication with the main fueloutlet. In some embodiments, the fuel membrane is also in fluidcommunication with the supplemental fuel inlet. In order to provide theair entrainment space described above, the fuel membrane can be spacedoutwardly from the exterior surface of the sidewall of the pre-mixchamber.

Depending on the particular configuration of the inventive flare burner,the pre-mix zone can consist of the pre-mix chamber alone or can includethe pre-mix chamber together with areas below and/or above the actualpre-mix chamber. For example, when the air inlet of the pre-mix chamberis in the bottom of the pre-mix chamber and the supplemental fuel inletis spaced below the air inlet, the fuel and air begin to mix below theair inlet and pre-mix chamber. Also, the fuel and air typically continueto mix above the air/fuel outlet disposed in the top of the pre-mixchamber prior to ignition and combustion in the combustion zone.

The pre-mix chamber and fuel membrane can be formed in a variety ofshapes and sizes. In one embodiment, the pre-mix chamber and fuelmembrane have a round cross-section. In another embodiment, the pre-mixchamber and fuel membrane have a rectangular cross-section.

In order to enhance the entrainment of air caused by injecting fuelthrough the supplemental fuel inlet into the pre-mix zone, the interiorsurface of the pre-mix chamber can include a section that is a Coandasurface. The supplemental fuel inlet is located in a position withrespect to the pre-mix chamber such that fuel can be injected from thesupplemental fuel inlet onto the Coanda surface. The fuel tends toadhere to and follow the path of the Coanda surface and form into arelatively thin film which causes more air to be entrained into thepre-mix chamber and better mixing of the air with the fuel to occur inthe pre-mix chamber.

The pre-mix chamber can have a length to inside hydraulic diameter ratioin the range of from about 0.25:1 to about 4:1. A unit with a pre-mixchamber having a length to inside hydraulic diameter ratio greater than4:1 would function with an added benefit but would generally be costprohibitive. In one embodiment, the pre-mix chamber has a length toinside hydraulic diameter ratio in the range of from about 1:1 to about3:1. In another embodiment, the pre-mix chamber has a length to insidehydraulic diameter ratio of about 1:1 or less. A relatively short lengthof the pre-mix chamber can be advantageous in ground flare and otherflare applications in which the length (or height) of the burner isimportant, or in applications in which highly reactive fuels might leadto internal burning. Also, in some configurations the fuel is injectedfrom the supplemental fuel inlet under conditions (for example, aplurality of small jets; high pressure) that allow a uniform mixture ofair and fuel to be achieved even when the pre-mix chamber has a very lowlength to inside hydraulic diameter ratio.

The inventive ground flare comprises a plurality of flare burners, afence or other enclosure extending around the flare burners and a fuelsupply line for supplying fuel to the flare burners. At least one of theflare burners is the inventive flare burner described above.

The invention also includes a method of flaring fuel with a flare burnerwherein the fuel to be flared is injected through a fuel outlet of theburner into a combustion zone and ignited to create a flame envelope andcombust the fuel. In accordance with the inventive method, a portion ofthe fuel is introduced into a pre-mix zone of the flare burner in amanner that entrains air into the pre-mix zone and creates a mixture ofair and fuel within the pre-mix zone. The mixture of air and fuel isinjected from the pre-mix zone into a central portion of the flameenvelope.

The amount of air entrained into the pre-mix zone and injected into thecentral portion of the flame envelope is preferably at least about 15%of the stoichiometric amount of air required to support combustion ofthe fuel introduced into the pre-mix zone. In some applications,injection of a “fuel-rich” mixture of fuel and air (i.e., a mixturehaving less than 100% of the stoichiometric amount of air required tosupport combustion of the fuel introduced into the pre-mix zone) intothe central portion of the flame envelope is suitable. In mostapplications, however, injection of a “lean” mixture of fuel and air(i.e., a mixture having more than 100% of the stoichiometric amount ofair required to support combustion of the fuel introduced into thepre-mix zone) into the central portion of the flame envelope is desired.In most applications, the amount of air entrained into the pre-mix zoneand injected into the central portion of the flame envelope is in therange of from about 125% to about 300% of the stoichiometric amount ofair required to support combustion of the fuel introduced into thepre-mix zone.

The amount of fuel introduced into the pre-mix zone is preferably in therange of from about 5% to about 50% of the total amount of fuel to beflared by the flare burner. Due to the injection of a pre-mixed fuelstream into a central portion of the flame envelope in accordance withthe inventive method, the flame envelope includes combustion at itscenter as well as its outer surface. The resulting toroidal flamecreates additional mixing and turbulence which results in more uniformand faster combustion of the flame envelope. As a result, the height ofthe flame envelope can be decreased or the volume of fuel that can beflared with a given flame envelope can be increased. Other advantagesare achieved by the inventive flare burner and method as well.

It is, therefore, a general object of the present invention to provide aflare burner and associated method by which a high volume of fuel can becombusted in a relatively short and uniform flame envelope.

Other and further objects, features and advantages of the presentinvention will be readily apparent to those skilled in the art upon areading of the description of preferred embodiments which follows whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation view of a prior art ground flare burner.

FIG. 2 is a top view of the flare burner shown by FIG. 1.

FIG. 3 is a general depiction of the flame envelope created by the priorart flare burner shown by FIGS. 1 and 2.

FIG. 4 is a perspective view of a first embodiment of the inventiveground flare burner.

FIG. 5 is a sectional view taken along the line 5-5 of FIG. 4.

FIG. 6 is a top view of the burner shown by FIGS. 4 and 5.

FIG. 7 is a sectional view taken along the line 7-7 of FIG. 6 andshowing optional risers or tip extensions.

FIG. 8 illustrates an alternative embodiment of an annular fuel injectorbody that can be utilized in association with the first, second andfourth embodiments of the inventive flare burner.

FIG. 9 is a perspective view of a second embodiment of the inventiveflare burner.

FIG. 10 is a sectional view taken along lines 10-10 of FIG. 11.

FIG. 10A illustrates an alternative embodiment of the annulardistribution manifold used in association with the second embodiment.

FIG. 11 is a top view of the flare burner shown by FIGS. 9 and 10.

FIG. 12 is a sectional view taken along lines 12-12 of FIG. 10.

FIG. 13 is a perspective view of a third embodiment of the inventiveflare burner.

FIG. 14 is a sectional view taken along lines 14-14 of FIG. 13.

FIG. 15 is a top view of the flare burner shown by FIGS. 13 and 14.

FIG. 16 is a sectional view taken along lines 16-16 of FIG. 13 andshowing optional risers or tip extensions.

FIG. 17 is a sectional view taken along lines 17-17 of FIG. 15.

FIG. 17A illustrates an alternative embodiment of the tubulardistribution manifolds used in association with the third embodiment.

FIG. 18 is a sectional view taken along lines 18-18 of FIG. 14.

FIG. 19 is a perspective view of a fourth embodiment of the inventiveflare burner.

FIG. 20 is a sectional view taken along lines 20-20 of FIG. 19.

FIG. 21 is a sectional view taken along lines 21-21 of FIG. 22 andshowing an optional component of the burner.

FIG. 22 is a top view of the burner shown by FIGS. 19-21.

FIG. 23 illustrates an alternative embodiment of the supplemental fuelinlet of the burner shown by FIGS. 19-22.

FIG. 24 is a general depiction of the flame envelope created by eachembodiment of the inventive flare burner.

FIG. 25 is a perspective view illustrating a modification that can bemade to each embodiment of the inventive flare burner.

FIG. 26 is a sectional view taken along lines 26-26 of FIG. 25.

FIG. 27 is a top view of the burner shown by FIGS. 25 and 26.

FIG. 28 is a general depiction of the flame envelope created by eachembodiment of the inventive flare burner as modified in the mannerillustrated by FIGS. 25-27.

FIG. 29 is a schematic illustration of one embodiment of the inventivethe ground flare.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and particularly to FIGS. 1-3, a priorart ground flare burner is illustrated and generally designated by thenumeral 10. The prior art burner 10 includes a burner casting 12attached to a fuel riser 14. The burner casting 12 includes a centralportion 15 and a plurality of fuel outlet arms 16 concentricallyarranged around the central portion and the top of the riser 14. Eachfuel outlet arm 16 includes one or more fuel ports 18. Fuel is provideddirectly to the fuel ports 18, that is, the fuel is not first pre-mixedwith air. As a result, the fuel jets created by the ports 18 arediffusion fuel jets.

FIG. 3 generally depicts a flame envelope 20 created by the burner 10.The fuel (generally depicted by black arrows) is injected into thecombustion zone 22 through the ports 18 at a high velocity which drawsair into the jets. Air from the surrounding environment is laterallyentrained from above the discharge point of the fuel. As the velocity ofthe stream is diminished, the buoyancy effect of the hot gases thencontributes to the overall mixing regimen of the fuel which allowscombustion to be completed. The overall flame envelope 20 has a length23 and includes a dense, central core of fuel 24. The central core offuel 24 remains un-oxidized until the outer portions 26 of the flame 22begin to burn off. Although the central portion of the flame envelopemay include some air pockets 28, the amount of air in the air pockets isnot sufficient to support homogenous combustion of the central core offuel 24. The dense, central core of fuel 24 generally remains intactuntil sufficient attrition of the outer portions 26 of the fuel occursto allow sufficient amounts of air to enter the inner confines of theflame envelope and allow completion of the oxidation process.Unfortunately, the dense core of fuel 24 in the center of the flameenvelope 20 makes it difficult to increase the flow rate of the fuel tosupport a larger flame without causing the length of the flame toincrease and/or smoke to occur.

The Inventive Flare Burner

Referring now to FIGS. 4-8, one embodiment of the inventive flare burneris illustrated and generally designated by the numeral 30. The flareburner 30 comprises a pre-mix zone 31 including a pre-mix chamber 32,and a supplemental fuel inlet 34 for injecting fuel into the pre-mixzone, a main fuel outlet 36 and a fuel feed conduit 38. As used hereinand in the appended claims, “fuel” means the waste gas, diverted fuelstock and/or other gas or liquid to be flared by the inventive flareburner, flare apparatus (for example, the inventive ground flareapparatus) and method. Liquids can form, for example, when the partialpressure of heavy unsaturated or saturated fuels is at or belowsaturated conditions. As shown by FIG. 4, a pilot 40 may be associatedwith the burner 30 (as well as the burners 130, 230 and 330 describedbelow) to initially ignite the fuel and air mixture that is dischargedby the burner.

In the embodiment illustrated by FIGS. 4-8, the pre-mix chamber 32 ofthe flare burner 30 provides the predominant portion of the pre-mix zone31. A mixture (preferably a substantially homogenous mixture) of fueland air can be formed in the pre-mix zone 31 including the pre-mixchamber 32. As discussed below, the mixture formed in the pre-mix zone31 can be either fuel-rich or fuel-lean. The pre-mix chamber 32 includesa round cross-section and has a cylindrical shape. The pre-mix chamberincludes a top 42, a bottom 44, a sidewall 46 connecting the top to thebottom, an air inlet 48 disposed in the bottom 44 and an air/fuel outlet50 disposed in the top 42. As shown, the top 42 and bottom 44 are openthereby forming the air inlet 48 and air/fuel outlet 50. As a result,the air inlet 48 and air/fuel outlet 50 each also have a roundcross-section. A lower portion 52 of the pre-mix chamber 32 is flaredoutwardly to impart a bell (well-rounded) shape to the lower section toenhance the rate of flow of the incoming fuel and air. Alternatively,the lower portion 52 of the pre-mix chamber 32 is not flared outwardly,i.e., the entire pre-mix chamber has a uniform cylindrical shape. Asbest shown by FIG. 5, the pre-mix zone 31 includes a pre-mix space 31(a)below the pre-mix-chamber 32 (between the supplemental fuel inlet 34 andthe bottom 44 and air inlet 48 of the pre-mix chamber), the interior31(b) of the pre-mix chamber, and a pre-mix space 31(c) immediatelyabove the top 42 and air/fuel outlet 50 of the pre-mix chamber. In theembodiment shown by FIGS. 4-9, the primary mixing of the pre-mix air andfuel occurs in the interior 31(b) of the pre-mix chamber 32 and in thepre-mix space 31(c).

The pre-mix chamber 32 has a length (or height) to inside hydraulicdiameter ratio in the range of from about 0.25:1 to about 4:1,preferably about 1:1 to about 3:1. The exact ratio of the length (orheight) to inside hydraulic diameter of the pre-mix chamber 32 willdepend in part on the type of fuel to be flared and the pressureavailable for entrainment and mixing. Generally, a longer pre-mixchamber can result in better mixing of fuel and air therein; however,this advantage is balanced against cost and other considerations. In apreferred embodiment, the length (or height) to inside hydraulicdiameter ratio of the pre-mix chamber 32 is approximately 1.5:1. As usedherein and in the appended claims, “inside hydraulic diameter” meansfour (4) times the area within the pre-mix chamber divided by theperimeter of the interior surface of the sidewall of the pre-mixchamber.

The supplemental fuel inlet 34 is located in a position with respect tothe pre-mix zone 31 such that the injection of fuel from thesupplemental fuel inlet into the pre-mix zone entrains air into thepre-mix space 31(a) and through the air inlet 48 into the pre-mixchamber 32 whereby a mixture, preferably a substantially homogenousmixture, of fuel and air is formed in the pre-mix zone and caused toexit the air/fuel outlet 50 in the top 42 of the pre-mix chamber. Thefuel and air continue to mix in the pre-mix space 31(c). Combustion ofthe mixture of fuel and air does not typically occur until the mixtureexits the air/fuel outlet 50, generally a detached distance from theair/fuel outlet. The distance from the air/fuel outlet 50 at whichcombustion occurs varies due to the amount of air in the mixture and thevelocity at which the mixture is discharged from the air/fuel outlet. Insome cases, due to short de-stage timing sequences, combustion can occurin the pre-mix zone (for example, in short duration, very low pressurescenarios). As shown by FIGS. 6 and 7, the supplemental fuel inlet 34comprises a central fuel injector 54 having one or more fuel ports 58therein.

An annular fuel membrane 60 is disposed around the outside perimeter ofthe pre-mix chamber 32. The fuel membrane 60 is connected to the fuelfeed conduit 38 and in fluid communication with the main fuel outlet 36.The fuel membrane 60 comprises an open top 62, a bottom 64, and anexternal sidewall 66 and internal sidewall 67 connecting the top to thebottom. In the embodiment shown by FIGS. 4-8, the internal sidewall 67of the membrane 60 is also the sidewall 46 of the pre-mix chamber 32. Anannular seal 68 is attached to the bottom 64 of the fuel membrane 60 andextends around the sidewall 46 of the pre-mix chamber 32 to ensure theintegrity of the membrane. In an alternate embodiment, as exemplified byFIGS. 25-28 and explained below, the fuel membrane 60 can be spacedoutwardly from the sidewall 46 of the pre-mix chamber 32 in order toprovide an annular space between the exterior surface of the sidewall 46and the main fuel outlet 36. The annular space allows air to beentrained from below the burner to a point adjacent to the fuel ports 74disposed on an inner portion of the main fuel outlet 36. In thisembodiment, the internal sidewall 67 of the membrane 60 is separate fromthe sidewall 46 of the pre-mix chamber 32.

The main fuel outlet 36 is located in a position with respect to the top42 of the pre-mix chamber such that fuel can be injected from the mainfuel outlet 36 around the perimeter 69 of the air/fuel outlet 50 of thepre-mix chamber. As best shown by FIG. 6, the main fuel outlet 36comprises a flat, annular fuel injector body 70 having a plurality offuel ports 74 therein. The fuel jets created by the ports 74 arediffusion fuel jets. The annular fuel injector body 70 is attached tothe open top 62 of the annular membrane 60 such that the fuel ports 74are disposed around the perimeter 69 of the air/fuel outlet 50 of thepre-mix chamber. The inside and outside diameters of the annularmembrane 60 and annular fuel injector body 70 are approximately thesame. Fuel can be annularly injected from the main fuel outlet 36 (i.e.,the annular fuel injector body 70) around the perimeter 69 of theair/fuel outlet 50. The ports 74 can be sized and spaced to control themanner (e.g., direction and velocity) in which the fuel is injected fromthe ports. This feature in conjunction with the flow of fuel and airthrough the air/fuel outlet 50 allows the shape and length of theoverall flame envelope to be controlled.

As shown by FIG. 7, if desired, the diffusion fuel ports 74 can bespaced from the fuel injector body 70 by a plurality of correspondingshort gas risers or tip extensions 76. Spacing the ports 74 from thefuel injector body 70 with the risers 76 can result in better lateralentrainment of air in some applications. The risers also allow theconfigurations of the ports and resulting fuel flow properties to bemechanically changed if necessary.

An alternative embodiment of the annular fuel injector body 70 is shownby FIG. 8. In this embodiment, a plurality of fuel ports 74 isstrategically spaced around the outside, inside and middle of the fuelinjector body 70. Spacing of the fuel ports 74 around the fuel injectorbody 70 in this manner allows entrainment corridors between the jets tobe utilized for better mixing and entrainment. As understood by thoseskilled in the art, the injector body 70 can include various iterationsof the ports 74. The particular port configuration utilized will dependon various factors including the type of fuel to be flared (includingthe molecular weight, heating value, stoichiometry and temperature ofthe stream) and available pressure in connection therewith.

The fuel feed conduit 38 is in fluid communication with the supplementalfuel inlet 34 and the main fuel outlet 36 for conducting fuel thereto.The fuel feed conduit 38 includes a main branch 80 having a first end 82and a second end 84. The first end 82 includes a flange 86 forconnecting the first end to a source of the fuel (as understood by thoseskilled in the art, these types of connections are more typically madeby welding the pipe sections directly together or with some othermechanical connection that does not require gaskets; e.g., the gasketsbetween corresponding flanges generally cannot withstand the radiantheat in the surrounding environment). The second end 84 is connected toa corresponding inlet 88 in the external sidewall 66 of the fuelmembrane 60. The fuel feed conduit 38 also includes a supplementalbranch 90 which connects the fuel feed conduit to the supplemental fuelinlet 34. The supplemental branch 90 includes a first end 92 and asecond end 94. The first end 92 is connected to the main branch 90 ofthe feed conduit 38. A coupling 96 connects the second end 94 to thesupplemental fuel inlet 34. Alternatively, separate fuel feed conduitsor risers can conduct fuel to the supplemental fuel inlet 34 and mainfuel outlet 36 (as opposed to the single integrated conduit or riser38). The separate conduits or risers will typically run from a commonfuel header.

Referring to FIG. 5, operation of the flare burner 30 will be described.A portion of the fuel to be flared (generally depicted by black arrows)is conducted through the main branch 80 of the fuel feed conduit 38 tothe fuel membrane 60 and to the main fuel outlet 36. A portion of thefuel to be flared is also conducted from through the supplemental branch90 of the fuel feed conduit 38 to the supplemental fuel inlet 34. Theinjection of fuel from the supplemental fuel inlet 34 into the pre-mixzone 31 and pre-mix chamber 32 entrains air into the pre-mix space 31(a)and through the air inlet 48 into the interior 31(b) of the pre-mixchamber whereby a mixture (preferably a substantially homogenousmixture) of fuel and air is formed in the pre-mix zone and caused toexit the air/fuel outlet 50. The fuel and air continue to mix for ashort distance above the air/fuel outlet 50. The remaining fuel to beflared is annularly injected from the main fuel outlet 36 around theperimeter 69 of the air/fuel outlet 50 of the pre-mix chamber and hencearound the air/fuel mixture exiting the air/fuel outlet of the pre-mixchamber. The burner is preferably designed and operated in a manner suchthat the amount of air entrained into the pre-mix zone 31 including thepre-mix chamber 32 is in excess of the stoichiometric amount of airrequired to combust the fuel injected into the pre-mix zone. The excessair is imparted to the center of the flame envelope for combustion offuel therein. As explained further below, however, in some applicationsthe burner is designed and operated in a manner such that the amount ofair entrained into the pre-mix zone 31 including the pre-mix chamber 32is equal to or less than the stoichiometric amount of air required tocombust the fuel injected into the pre-mix zone (although it is stillflammable). The injection of a “fuel-rich” mixture of fuel and air(i.e., a mixture having less than the stoichiometric amount of airrequired to support combustion of the fuel introduced into the pre-mixzone) into the central portion of the flame envelope is desirable insome applications.

FIG. 24 generally depicts the flame envelope 100 created by the flareburner 30 (as well as the burners 130, 230 and 330 described below). Asshown, excess air is injected from the pre-mix chamber 32 into a centerportion 102 of the flame envelope 100. The excess air, depicted by airpockets 103 in FIG. 24 mixes with fuel in the center portion 102 of theflame envelope 100 to form, in effect, two initial zones offlammability, zone 104(a) and 104(b). The fuel in the center portion 102of the flame would otherwise not encounter oxidizer (air) until theouter portions 105 of the flame envelope begin to combust, allowing thenext layers of fuel access to the air. Supplying air to the centerportion 102 of the flame envelope 100 not only creates a middle zone offlammability but also breaks the flame apart as the inner combustionzone expands under the heat of combustion. The addition of a distinctcombusting flame inside the larger main flame adds significantturbulence to enhance mixing and break up the central core of fuel. As aresult, more uniform and faster combustion of the flame envelope occurswhich shortens the overall length of the flame or allows significantlymore fuel to be flared with the same flame length. As the amount ofexcess air imparted to the center portion 102 of the flame envelope 100increases, the length of the flame decreases or the volume of fuel thatcan be flared at a given flame height increases. For example, as shownby FIG. 24, the flame envelope 100 has a length 106 that issubstantially less for the same amount of fuel than the length 23 of theprior art flame envelope 20 shown by FIG. 3.

Referring now to FIGS. 9-12, a second embodiment of the inventive flareburner is illustrated and generally designated by the reference numeral130. Like the other embodiments of the inventive flare burner, the flareburner 130 comprises a pre-mix zone 131 including a pre-mix chamber 132,and a supplemental fuel inlet 134 for injecting fuel into the pre-mixzone, a main fuel outlet 136 and a fuel feed conduit 138. A pilot (asshown by FIG. 4) may be associated with the burner 130 to initiallyignite the fuel and air mixture that is discharged by the burner.

In the embodiment illustrated by FIGS. 9-12, the pre-mix chamber 132 ofthe flare burner 130 provides the predominant portion of the pre-mixzone 131. A mixture (preferably a substantially homogenous mixture) offuel and air can be formed in the pre-mix zone 131 including the pre-mixchamber 132. As discussed below, the mixture formed in the pre-mix zone131 can be either fuel-rich or fuel-lean. The pre-mix chamber 132includes a round cross-section and has a cylindrical shape. It includesa top 142, a bottom 144, a sidewall 146 connecting the top to thebottom, an air inlet 148 disposed in the bottom 144 and an air/fueloutlet 150 disposed in the top. As shown, the top 142 and bottom 144 areopen thereby forming the air inlet 148 and air/fuel outlet 150. As aresult, the air inlet 148 and air/fuel outlet 150 each also have a roundcross-section.

As best shown by FIG. 10, the pre-mix zone 131 includes a pre-mix space131(a) below the pre-mix-chamber 132 (between the supplemental fuelinlet 134 and the bottom 144 and air inlet 148 of the pre-mix chamber),the interior 131(b) of the pre-mix chamber, and a pre-mix space 131(c)immediately above the top 142 and air/fuel outlet 150 of the pre-mixchamber. In the embodiment shown by FIGS. 9-12, the primary mixing ofthe air and fuel occurs in the interior 131(b) of the pre-mix chamber132 and in the pre-mix space 131(c). The sidewall 146 of the pre-mixchamber 132 includes an interior surface 154 and an exterior surface156. A lower section 158 of the sidewall 146 is flared outwardly in acurvilinear manner to impart an annular Coanda surface 160 to theinterior surface 154 of the sidewall.

The pre-mix chamber 132 has a length (or height) to inside hydraulicdiameter ratio in the range of from about 0.25:1 to 4:1, preferablyabout 1:1 to about 3:1. The exact ratio of the length (or height) toinside hydraulic diameter of the pre-mix chamber 132 will depend in parton the type of fuel to be flared and the pressure available forentrainment and mixing. Generally, a longer pre-mix chamber can resultin better mixing of fuel and air therein; however, this advantage isbalanced against cost and other considerations. In a preferredembodiment, the length (or height) to inside hydraulic diameter ratio ofthe pre-mix chamber 132 is approximately 1.5:1.

The supplemental fuel inlet 134 is located in a position with respect tothe pre-mix zone 131 such that the injection of fuel from thesupplemental fuel inlet into the pre-mix zone entrains air into thepre-mix space 131(a) and through the air inlet 148 into the pre-mixchamber whereby a mixture, preferably a substantially homogenousmixture, of fuel and air is formed in the pre-mix zone and caused toexit the air/fuel outlet 150 in the top 142 of the pre-mix chamber. Thefuel and air continue to mix in the pre-mix space 131(c). Combustion ofthe mixture of fuel and air does not typically occur until the mixtureexits the air/fuel outlet 150, generally a detached distance from theair/fuel outlet. The distance from the air/fuel outlet 150 at whichcombustion occurs varies due to the amount of air in the mixture and thevelocity at which the mixture is discharged from the air/fuel outlet. Insome cases, due to short de-stage timing sequences, combustion can occurin the pre-mix zone (for example, in short duration, very low pressurescenarios). As shown by FIGS. 10 and 12, the supplemental fuel gas inlet134 comprises an annular distribution manifold 164 having a plurality offuel ports 166 therein. The fuel ports 166 are substantially roundapertures. As shown by FIG. 10, the annular distribution manifold 164 islocated in a position with respect to the pre-mix chamber 132 such thatfuel can be annularly injected from the manifold 164 onto the annularCoanda surface 160.

FIG. 10A illustrates an alternative embodiment of the annulardistribution manifold 164. In this embodiment, the fuel ports 166 areelongated apertures or slots. The slotted shape of the fuel ports 166causes the fuel to be injected onto the annular Coanda surface 160 in asheeted pattern which serves to enhance the entrainment and mixingeffect created by the Coanda surface and allows the fuel to be injectedfrom the manifold 164 at a higher rate. If desired, the slots 166 can beconnected to form continuous elongated apertures or slots in thedistribution manifold 164.

An annular fuel membrane 170 is disposed around the outside perimeter ofthe pre-mix chamber 132. The fuel membrane 170 is connected to the fuelfeed conduit 138 and in fluid communication with both the main fueloutlet 136 and the supplemental fuel inlet 134. The fuel membrane 170comprises an open top 172, a bottom 174, and an external sidewall 176and internal sidewall 177 connecting the top to the bottom. In theembodiment shown by FIGS. 9-12, the internal sidewall 177 is also thesidewall 146 of the pre-mix chamber. An annular seal 178 is attached tothe bottom 174 of the fuel membrane 170 and extends around the sidewall146 of the pre-mix chamber 132 to ensure the integrity of the membrane.In an alternate embodiment, as exemplified by FIGS. 25-28 and explainedbelow, the fuel membrane 170 can be spaced outwardly from the sidewall146 of the pre-mix chamber 132 in order to provide an annular spacebetween the exterior surface of the sidewall 146 and the main fueloutlet 136. The annular space allows air to be entrained from below theburner to a point adjacent to the fuel ports 192 disposed on an innerportion of the main fuel outlet 136. In this embodiment, the internalsidewall 177 of the membrane 170 is separate from the sidewall 146 ofthe pre-mix chamber 132.

Supplemental fuel feed conduits 180(a), 180(b), 180(c) and 180(d) extendfrom the annular fuel membrane 170 to the supplemental fuel inlet 134(i.e., to the annular distribution manifold 164) to deliver fuel fromthe fuel membrane 170 to the inlet 134 (i.e., the manifold 164). Each ofthe supplemental fuel feed conduits 180(a), 180(b), 180(c) and 180(d)includes a first end 182 attached to the membrane 170 and a second end184 attached to the inlet 134 (i.e., the manifold 164).

The main fuel outlet 136 is located in a position with respect to thetop 142 of the pre-mix chamber 132 such that fuel can be injected fromthe main fuel outlet around the perimeter 186 of the air/fuel outlet 150of the pre-mix chamber. As best shown by FIG. 11, the main fuel outlet136 comprises a flat, annular fuel injector body 188 having a pluralityof fuel ports 192 therein. The fuel jets created by the ports 192 arediffusion fuel jets. The annular fuel injector body 188 is attached tothe open top 172 of the annular membrane 170 such that the fuel ports192 are disposed around the perimeter 186 of the air/fuel outlet 150 ofthe pre-mix chamber 132. The inside and outside diameters of the annularmembrane 170 and annular fuel injector body 188 are approximately thesame. Fuel can be annularly injected from the main fuel outlet 136(i.e., the annular fuel injector body 188) around the perimeter 186 ofthe air/fuel outlet 150. The ports 192 can be sized and spaced tocontrol the manner (e.g., direction and velocity) in which the fuel isinjected from the ports. This feature in conjunction with the flow offuel and air through the air/fuel outlet 150 allows the shape and lengthof the overall flame envelope to be controlled.

As shown by FIG. 7, if desired, the diffusion fuel ports 192 can bespaced from the fuel injector body 188 by a plurality of correspondingshort gas risers or tip extensions 196. Spacing the ports 192 from thefuel injector body 188 with the risers 196 can result in better lateralentrainment of air in some applications. The risers also allow theconfigurations of the ports and resulting fuel flow properties to bemechanically changed if necessary. The alternative embodiment of thefuel injector body 70 shown by FIG. 8 may also be used in lieu of theannular fuel injector body 188. As understood by those skilled in theart, the injector body 188 can include various iterations of the ports192. The particular port configuration utilized will depend on variousfactors including the type of fuel to be flared (including the molecularweight, heating value, stoichiometry and temperature of the stream) andavailable pressure in connection therewith.

The fuel feed conduit 138 is in fluid communication with thesupplemental fuel inlet 134 and the main fuel outlet 136 for conductingfuel thereto. The fuel feed conduit 138 has a first end 200 and a secondend 202. The first end 200 includes a flange 204 for connecting thefirst end to a source of the fuel (again, these types of connections aremore typically made by welding). The second end 202 is connected to acorresponding inlet 206 in the external sidewall 176 of the annular gasmembrane 170. Alternatively, separate fuel feed conduits or risers canconduct fuel to the supplemental fuel inlet 134 and main fuel outlet 136(as opposed to the single integrated conduit or riser 138). The separateconduits or risers will typically run from a common fuel header.

Referring to FIG. 10, operation of the burner 130 will be described.Fuel to be flared (generally depicted by black arrows) is conductedthrough the fuel feed conduit 138 to the annular gas membrane 170. Aportion of the fuel is conducted by the fuel membrane 170 to the mainfuel outlet 136 (i.e., the annular injector body 188). The remainingportion of the fuel is conducted by the membrane 170 through the fuelfeed conduits 180(a), 180(b), 180(c) and 180(d) to the supplemental fuelinlet 134 (i.e., the annular distribution manifold 164). Fuel isinjected from the fuel ports 166 of the annular distribution manifold164 through the pre-mix space 131(a) onto the annular Coanda surface 160on the interior surface 154 of the pre-mix chamber 132. The injection offuel from the gas ports 166 into the pre-mix zone 131 and pre-mixchamber 132 entrains air into the pre-mix space 131(a) and through theair inlet 148 into the interior 131(b) of the pre-mix chamber whereby amixture (preferably a substantially homogenous mixture) of fuel and airis formed in the pre-mix zone and caused to exit the air/fuel outlet150. The fuel and air continue to mix for a short distance above theair/fuel outlet 150. Injection of the fuel from the fuel ports 166 ontothe Coanda surface 160 causes the fuel to adhere to and follow the pathof the Coanda surface and form into a relatively thin film which resultsin a more efficient entrainment of the air and mixing of the air withthe fuel. The fuel to be flared is injected from the main fuel outlet136 (the annular injector body 188) around the perimeter 186 of theair/fuel outlet 150 of the pre-mix chamber 132 and hence around theair/fuel mixture exiting the air/fuel outlet 150 of the pre-mix chamber.The flare burner 130 is preferably designed and operated in a mannersuch that the amount of air entrained into the pre-mix zone 131including the pre-mix chamber 132 is in excess of the stoichiometricamount of air required to combust the fuel injected into the pre-mixzone. The excess air is imparted to the center of the flame envelope forcombustion of fuel therein. As explained further below, however, in someapplications the burner is designed and operated in a manner such thatthe amount of air entrained into the pre-mix zone 131 including thepre-mix chamber 132 is equal to or less than the stoichiometric amountof air required to combust the fuel injected into the pre-mix zone. Theinjection of a “fuel-rich” mixture of fuel and air (i.e., a mixturehaving less than the stoichiometric amount of air required to supportcombustion of the fuel introduced into the pre-mix zone) into thecentral portion of the flame envelope is desirable in some applications.

The flare burner 130 achieves the same advantages that are achieved bythe flare burner 30. The flame envelope 100 generally depicted by FIG.24 is also created by the flare burner 130.

Referring now to FIGS. 13-18, a third embodiment of the inventive flareburner is illustrated and generally designated by the reference numeral230. Like the other embodiments of the inventive flare burner, the flareburner 230 comprises a pre-mix zone 231 including a pre-mix chamber 232,and a supplemental fuel inlet 234 for injecting fuel into the pre-mixzone, a main fuel outlet 236 and a fuel feed conduit 238. A pilot (asshown by FIG. 4) may be associated with the burner 130 to initiallyignite the fuel and air mixture that is discharged by the burner.

In the embodiment illustrated by FIGS. 13-18, the pre-mix chamber 232 ofthe flare burner 230 provides the predominant portion of the pre-mixzone 231. A mixture (preferably a substantially homogenous mixture) offuel and air can be formed in the pre-mix zone 231 including the pre-mixchamber 232. As discussed below, the mixture formed in the pre-mix zone231 can be either fuel-rich or fuel-lean. The pre-mix chamber 232includes a rectangular cross-section and has a rectangular shape. Itincludes a top 242, a bottom 244, a sidewall 246 connecting the top tothe bottom, an air inlet 248 disposed in the bottom 244 and an air/fueloutlet 250 disposed in the top. As shown, the top 242 and bottom 244 areopen thereby forming the air inlet 248 and air/fuel outlet 250. As aresult, the air inlet 248 and air/fuel outlet 250 each also have arectangular cross-section.

As best shown by FIG. 14, the pre-mix zone 231 includes a pre-mix space231(a) below the pre-mix-chamber 232 (between the supplemental fuelinlet 234 and the bottom 244 and air inlet 248 of the pre-mix chamber),the interior 231(b) of the pre-mix chamber, and a pre-mix space 231(c)immediately above the top 242 and air/fuel outlet 250 of the pre-mixchamber. In the embodiment shown by FIGS. 13-18, the primary mixing ofthe air and fuel occurs in the interior 31(b) of the pre-mix chamber 232and in the pre-mix space 231(c).

The sidewall 246 of the pre-mix chamber 232 includes four sides 246(a),246(b), 246(c) and 246(d). Each of the sides 246(a), 246(b), 246(c) and246(d) includes an interior surface 254 and an exterior surface 256. Alower portion 258 of each of the sides 246(a), 246(b), 246(c) and 246(d)is flared outwardly in a curvilinear manner to impart an annular Coandasurface 260 to the interior surface 254 of the side. The pre-mix chamber232 has a length (or height) to inside hydraulic diameter ratio in therange of from about 0.25:1 to 4:1, preferably about 1.1 to about 3:1.The exact ratio of the length (or height) to inside hydraulic diameterof the pre-mix chamber 232 will depend in part on the type of fuel to beflared and the pressure available for entrainment and mixing. Generally,a longer pre-mix chamber can result in better mixing of fuel and airtherein; however, this advantage is balanced against cost and otherconsiderations. In a preferred embodiment, the length (or height) toinside hydraulic diameter ratio of the pre-mix chamber 232 isapproximately 1.5:1.

The supplemental fuel inlet 234 is located in a position with respect tothe pre-mix zone 231 such that the injection of fuel from thesupplemental fuel inlet into the pre-mix zone entrains air into thepre-mix space 231(a) and through the air inlet 248 into the pre-mixchamber 232 whereby a mixture, preferably a substantially homogenousmixture, of fuel gas and air is formed in the pre-mix zone and caused toexit the air/fuel outlet 250 in the top 242 of the pre-mix chamber.Combustion of the mixture of fuel and air does not typically occur untilthe mixture exits the air/fuel outlet 250, generally a detached distancefrom the air/fuel outlet. The distance from the air/fuel outlet 250 atwhich combustion occurs varies due to the amount of air in the mixtureand the velocity at which the mixture is discharged from the air/fueloutlet. In some cases, due to short de-stage timing sequences,combustion can occur in the pre-mix zone (for example, in shortduration, very low pressure scenarios).

As best shown by FIG. 18, the supplemental fuel inlet 234 comprises twotubular distribution manifolds 264(a) and 264(b), each having aplurality of fuel ports 266 therein. The fuel ports 266 aresubstantially round apertures. The distribution manifold 264(a) islocated in a position with respect to the pre-mix chamber 232 such thatfuel can be injected from the manifold 264(a) onto the Coanda surface260 on the interior surface 254 of the side 246(a). Similarly, thedistribution manifold 264(b) is located in a position with respect tothe pre-mix chamber 232 such that fuel can be injected from the manifold264(b) onto the Coanda surface 260 on the interior surface 254 of theopposing side 246(c). As understood by those skilled in the art, avariety of configurations of fuel ports and jets can be utilized toinject the fuel onto the Coanda surfaces in this embodiment. The numberand spacing of fuel ports, for example, can vary depending on thedesired thickness of the film to be created on the Coanda surfaces.

FIG. 17A illustrates an alternative embodiment of each of the tubulardistribution manifolds 264(a) and 264(b). In this embodiment, the fuelports 266 are elongated apertures or slots. The slotted shape of thefuel ports 266 causes the fuel to be injected onto the annular Coandasurface 260 in a sheeted pattern which serves to enhance the entrainmentand mixing effect created by the Coanda surface and allows a highervolume of gas to be flared. If desired, the slots 266 can be connectedto form continuous elongated apertures or slots in the distributionmanifolds 264(a) and 264(b). In addition to round apertures and slots,the fuel ports 266 can be formed in other shapes as well depending onthe particular application. Examples of other shapes include elongatedovals and rectangular slots.

A rectangular fuel membrane 270 is disposed around the outside perimeterof the pre-mix chamber 232. The fuel membrane 270 is connected to thefuel feed conduit 238 and in fluid communication with both the main fueloutlet 236 and the supplemental fuel inlet 234. The membrane 270comprises an open top 272, a bottom 274, and an external sidewall 276and internal sidewall 277 connecting the top to the bottom. In theembodiment shown by FIGS. 13-18, the internal sidewall 277 is also thesidewall 246 of the pre-mix chamber. A matching seal mechanism 278 isattached to the bottom 274 of the fuel membrane 270 and extends aroundthe sidewall 246 of the pre-mix chamber 232 to ensure the integrity ofthe membrane. In an alternate embodiment, as exemplified by FIGS. 25-28and explained below, the fuel membrane 270 can be spaced outwardly fromthe exterior surfaces 256 of the sides 246(a), 246(b), 246(c) and 246(d)of the sidewall 246 of the pre-mix chamber 232 in order to provide aspace between the exterior surface of the sidewall 246 and the main fueloutlet 236. The space allows air to be entrained from below the burnerto a point adjacent to the fuel ports 292 disposed on an inner portionof the main fuel outlet 236. In this embodiment, the internal sidewall277 of the membrane 270 is separate from the sidewall 246 of the pre-mixchamber 232.

Supplemental fuel feed conduits 280(a), 280(b), 280(c) and 280(d) extendfrom the fuel membrane 270 to the supplemental fuel inlet 234, that isto the tubular distribution manifolds 264(a) and 264(b), to deliver fuelfrom the fuel membrane thereto. Each of the supplemental fuel feedconduits 280(a), 280(b), 280(c) and 280(d) includes a first end 282attached to the fuel membrane 270 and a second end 284. The second ends284 of the conduits 280(a) and 280(d) are attached to opposing ends ofthe tubular distribution manifold 264(a). The second ends 284 of theconduits 280(b) and 280(c) are attached to opposing ends of the tubulardistribution manifold 264(b).

The main fuel outlet 236 is located in a position with respect to thetop 242 of the pre-mix chamber 232 such that fuel can be injected fromthe main fuel outlet around the perimeter 286 of the air/fuel outlet 250of the pre-mix chamber. As best shown by FIG. 15, the main fuel outlet236 comprises a flat, rectangular fuel injector body 288 having aplurality of diffusion fuel ports 292 therein. The fuel jets created bythe ports 292 are diffusion fuel jets. The fuel injector body 288 isattached to the open top 272 of the fuel membrane 270 such that thediffusion fuel ports 292 are disposed around the perimeter 286 of theair/fuel outlet 250 of the pre-mix chamber 232. The inside and outsidediameters of the membrane 270 and fuel injector body 288 areapproximately the same. Fuel can be injected from the main fuel outlet236 (i.e., the fuel injector body 288) around the perimeter 286 of theair/fuel outlet 250. The ports 292 can be sized and spaced to controlthe manner (e.g., direction and velocity) in which the fuel is injectedfrom the ports. This feature in conjunction with the flow of fuel andair through the air/fuel outlet 250 allows the shape and length of theoverall flame envelope to be controlled.

As shown by FIG. 16, if desired, the diffusion fuel ports 292 can bespaced from the fuel injector body 288 by a plurality of correspondingshort gas risers or tip extensions 296. Spacing the ports 292 from thefuel injector body 288 with the risers 296 can result in better lateralentrainment of air in some applications. The risers also allow theconfigurations of the ports and resulting fuel flow properties to bemechanically changed if necessary. As understood by those skilled in theart, the injector body 288 can include various iterations of the ports292. The particular port configuration utilized will depend on variousfactors including the type of fuel to be flared (including the molecularweight, heating value, stoichiometry and temperature of the stream) andavailable pressure in connection therewith.

The fuel feed conduit 238 is in fluid communication with thesupplemental fuel inlet 234 and the main fuel outlet 236 for conductingfuel gas thereto. The fuel feed conduit 238 has a first end 300 and asecond end 302. As shown, the first end 300 includes a flange 304 forconnecting the first end to a source of the fuel gas (again, these typesof connections are more typically made by welding). The second end 302is connected to a corresponding inlet 306 in the external sidewall 276of the annular fuel membrane 270. Alternatively, separate fuel feedconduits or risers can conduct fuel to the supplemental fuel inlet 234and main fuel outlet 236 (as opposed to the single integrated conduit orriser 238). The separate conduits or risers will typically run from acommon fuel header.

Referring to FIG. 14, in operation of the burner 230, fuel to be flared(generally depicted by black arrows) is conducted through the fuel feedconduit 238 to the fuel membrane 270. A portion of the fuel is conductedby the fuel membrane 270 to the main fuel outlet 236 (and the fuelinjector body 288). The remaining portion of the fuel is conducted bythe membrane 270 through the fuel feed conduits 280(a), 280(b), 280(c)and 280(d) to the supplemental fuel inlet 234 (and the tubulardistribution manifolds 264(a) and 264(b) thereof). Fuel is injected fromthe fuel ports 266 of the distribution manifolds 264(a) and 264(b) ontothe Coanda surface 260 on the interior surface 254 of the sides 246(a)and 246(c) of the pre-mix chamber 232. The injection of fuel from thefuel ports 266 into the pre-mix zone 231 and pre-mix chamber 232entrains air into the pre-mix space 231(a) and through the air inlet 248into the interior 231(b) of the pre-mix chamber whereby a mixture(preferably a substantially homogenous mixture) of fuel and air isformed in the pre-mix zone and caused to exit the air/fuel outlet 250.The fuel and air continue to mix for a short distance above the air/fueloutlet 250. Injection of the fuel from the fuel ports 266 onto theCoanda surface 260 on the interior surface 254 of the sides 246(a) and246(c) causes the fuel to adhere to and follow the path of the Coandasurface and form into a relatively thin film thereon which results in amore efficient entrainment of the air and mixing of the air with thefuel. The fuel to be flared is injected from the main fuel outlet 236(and the annular fuel injector body 288) around the perimeter 286 of theair/fuel outlet 250 of the pre-mix chamber 232 and hence around theair/fuel mixture exiting the air/fuel outlet of the pre-mix chamber. Theflare burner 230 is preferably designed and operated in a manner suchthat the amount of air entrained into the pre-mix zone 231 including thepre-mix chamber 232 is in excess of the stoichiometric amount of airrequired to combust the fuel injected into the pre-mix zone. The excessair is imparted to the center of the flame envelope for combustion offuel therein. As explained further below, however, in some applicationsthe burner 230 is designed and operated in a manner such that the amountof air entrained into the pre-mix zone 231 including the pre-mix chamber232 is equal to or less than the stoichiometric amount of air requiredto combust the fuel injected into the pre-mix zone. The injection of a“fuel-rich” mixture of fuel and air (i.e., a mixture having less thanthe stoichiometric amount of air required to support combustion of thefuel introduced into the pre-mix zone) into the central portion of theflame envelope is desirable in some applications.

The flare burner 230 achieves the same advantages that are achieved bythe flare burners 30 and 130. The flame envelope 100 generally depictedby FIG. 24 is also created by the flare burner 230.

The polygonal (rectangular in the embodiment illustrated) shape of theflare burner 230 may allow more flexibility in spacing the flare burnersin a ground flare application. Also, such a shape may allow moreflexibility in how the fuel is directed from the diffusion gas ports 292due to the fact that the geometry can be rotated to change theinteraction zones.

Referring now to FIGS. 19-23, a fourth embodiment of the inventive flareburner is illustrated and generally designated by the numeral 330. Likethe other embodiments of the inventive flare burner, the flare burner330 comprises a pre-mix zone 331 including a pre-mix chamber zone 332,and a supplemental fuel inlet 334 for injecting fuel into the pre-mixzone, a main fuel outlet 336 and a fuel feed conduit 338. A pilot 40 (asshown by FIG. 4) may be associated with the burner 330 to initiallyignite the fuel and air mixture that is discharged by the burner.

A mixture (preferably a substantially homogenous mixture) of fuel andair can be formed in the pre-mix zone 331 including the pre-mix chamber332. As discussed below, the mixture formed in the pre-mix zone 331 canbe either fuel-rich or fuel-lean. The pre-mix chamber 332 includes around cross-section and has a cylindrical shape. The pre-mix chamberincludes a top 342, a bottom 344, a sidewall 346 connecting the top tothe bottom, an air inlet 348 disposed in the bottom 344 and an air/fueloutlet 350 disposed in the top 342. The sidewall 346 includes aninterior surface 347 and an exterior surface 349. As shown, the top 342and bottom 344 are open thereby forming the air inlet 348 and air/fueloutlet 350. As a result, the air inlet 348 and air/fuel outlet 350 eachalso have a round cross-section. The pre-mix chamber 332 has a length(or height) to inside hydraulic diameter ratio in the range of fromabout 0.25:1 to about 4:1.

In the embodiment shown by FIGS. 19, 20, 22 and 23 (which does notinclude the extension cylinder 400 discussed below), the pre-mix chamber332 has a length (or height) to inside hydraulic diameter ratio of about1:1 or less. Preferably, in the embodiment shown by FIGS. 19, 20, 22 and23 (which does not include the extension cylinder 400 discussed below),the pre-mix chamber 332 has a length (or height) to inside hydraulicdiameter ratio in the range of from about 0.25:1 to about 1:1. Asdiscussed above, a longer pre-mix chamber generally allows better mixingof the fuel and air in the pre-mix chamber to occur. However, it hasbeen discovered that the length (or height) of the pre-mix chamber 332,in the embodiment shown by FIGS. 19 and 20, is still sufficient for goodmixing to occur as long as the delay in ignition is conserved bytempering the flame propagation speed. As best shown by FIG. 20, thepre-mix zone 331 in this particular embodiment (which does not includethe extension cylinder 400 discussed below) includes a significantpre-mix space 331(a) below the pre-mix-chamber 332 (between thesupplemental fuel injector 334 and the bottom 344 and air inlet 348 ofthe pre-mix chamber), the interior 331(b) of the pre-mix chamber, and apre-mix space 331(c) immediately above the top 342 and air/fuel outlet350 of the pre-mix chamber. In this embodiment, mixing of the air andfuel occurs in all three sections of the pre-mix zone 331.

The supplemental fuel inlet 334 is located in a position with respect tothe pre-mix zone 331 such that the injection of fuel from thesupplemental fuel inlet into the pre-mix zone entrains air into thepre-mix space 331(a) and through the air inlet 348 into the pre-mixchamber 332 whereby a mixture, preferably a substantially homogenousmixture, of fuel gas and air is formed in the pre-mix zone and caused toexit the air/fuel outlet 350 in the top 342 of the pre-mix chamber.Combustion of the mixture of fuel and air does not typically occur untilthe mixture exits the air/fuel outlet 350, generally a detached distanceaway from the air/fuel outlet. The distance from the air/fuel outlet 350at which combustion occurs varies due to the amount of air in themixture and the velocity at which the mixture is discharged from theair/fuel outlet. In some cases, due to short de-stage timing sequences,combustion can occur in the pre-mix zone (for example, in shortduration, very low pressure scenarios).

As shown by FIGS. 19 and 22, the supplemental fuel inlet 334 comprises aburner casting 352 having a bull nose 353 and a plurality of fuel outletarms 354 concentrically arranged around the bull nose and centered belowthe air inlet 348 of the pre-mix chamber 332. The supplemental fuelinlet 334 is concentric with the air inlet 348 and pre-mix chamber 332.In the embodiment shown by FIGS. 19 and 20, the supplemental fuel inlet334 is spaced below the air inlet 348 of the pre-mix chamber 332. Thesupplemental fuel inlet 334 can be in the range of from zero to twoinches below the air inlet 348; preferably it is approximately one inchbelow the air inlet. The exact distance can vary depending on the typeof fuel being flared, the particular application, the permitted lengthof the flame envelope and other factors.

Each fuel outlet arm 354 and the bull nose 353 include a plurality offuel ports 356. The ports 356 are linearly arranged along thelongitudinal axis of each fuel outlet arm 354. An alternative embodimentof the supplemental fuel inlet 334 is shown by FIG. 23. In thisembodiment, each gas outlet arm 354 includes two rows of diffusion fuelports 356, each port in each row being aligned such that it is notdirectly across from a port in the adjacent row. The supplemental fuelinlet 334, including the fuel outlet arms 354, is intentionally small toallow as much interaction between the discharged fuel and entrained airas possible. The “bluff body” effect created by the size and shape ofthe inlet 334 is minimized, leaving a clean approach of the air to thedischarged fuel.

An annular fuel membrane 360 is disposed around the outside perimeter ofthe pre-mix chamber 332. The fuel membrane 360 is connected to the fuelfeed conduit 338 and in fluid communication with the main fuel outlet336. The membrane 360 comprises an open top 362, a bottom 364, and anexternal sidewall 366 and internal sidewall 367 connecting the top tothe bottom. In a preferred embodiment, the external sidewall 366 isspaced approximately three inches from the internal sidewall 367 (thisdistance depends on the nature of the fuel and the overall configurationof the burner). In the embodiment shown by FIGS. 19, 20, 22 and 23, theinternal sidewall 367 of the membrane 360 is also the exterior surface349 of the sidewall 346 of the pre-mix chamber 332. In an alternateembodiment, as exemplified by FIGS. 25-28 and explained below, the fuelmembrane 360 can be spaced outwardly from the exterior surface 349 ofthe sidewall 346 of the pre-mix chamber 332 in order to provide anannular space between the exterior surface 349 of the sidewall 246 andthe main fuel outlet 336. The space allows air to be entrained frombelow the burner to a point adjacent to the fuel ports 374 disposed onan inner portion of the main fuel outlet 336. In this embodiment, theinternal sidewall 367 of the membrane 360 is separate from the sidewall346 of the pre-mix chamber 332.

The main fuel outlet 336 is located in a position with respect to thetop 342 of the pre-mix chamber such that fuel can be injected from themain fuel outlet 336 around the perimeter 368 of the air/fuel outlet 350of the pre-mix chamber. As best shown by FIG. 22, the main fuel outlet336 comprises a flat, annular fuel injector body 370 having a pluralityof fuel ports 374 therein. The fuel jets created by the ports 374 arediffusion fuel jets. The ports 374 are preferably spaced at six degreeincrements, although the spacing can vary depending on the particularapplication. The annular fuel injector body 370 is attached to the opentop 362 of the annular membrane 360 such that the fuel ports 374 aredisposed around the perimeter 368 of the air/fuel outlet 350 of thepre-mix chamber. The inside and outside diameters of the annularmembrane 360 and fuel injector body 370 are approximately the same. Fuelcan be annularly injected from the main fuel outlet 336 (i.e., the fuelinjector body 370) around the perimeter 368 of the air/fuel outlet 350.The ports 374 can be sized and spaced to control the manner (e.g.,direction and velocity) in which the fuel is injected from the ports.This feature in conjunction with the flow of fuel and air through theair/fuel outlet 350 allows the shape and length of the overall flameenvelope to be controlled.

As shown by FIG. 7, if desired, the diffusion fuel ports 374 can bespaced from the fuel injector body 370 by a plurality of correspondingshort gas risers or tip extensions 376. Spacing the ports 374 from thefuel injector body 370 with the risers 376 can result in better lateralentrainment of air in some applications. The risers also allow theconfigurations of the ports and resulting fuel flow properties to bemechanically changed if necessary. As understood by those skilled in theart, the fuel injector body 370 can include various iterations of theports 374. The particular port configuration utilized will depend onvarious factors including the type of fuel to be flared (including themolecular weight, heating value, stoichiometry and temperature of thestream) and available pressure in connection therewith.

The fuel feed conduit 338 is in fluid communication with thesupplemental fuel inlet 334 and the main fuel outlet 336 for conductingfuel thereto. The fuel feed conduit 338 includes a main branch 380having a first end 382 and a second end 384. The first end 382 includesa flange 386 for connecting the first end to a source of the fuel(again, these types of connections are more typically made by welding).The second end 384 is connected to a corresponding inlet 388 in theexternal sidewall 366 of the fuel membrane 360. The fuel feed conduit338 also includes a supplemental branch 390 which connects the fuel feedconduit to the supplemental fuel inlet 334. The supplemental branch 390includes a first end 392 and a second end 394. The first end 392 isconnected to the main branch 390 of the feed conduit 338. The second end394 is connected to the supplemental fuel inlet 334 (specifically thecasting 352). Alternatively, separate fuel feed conduits or risers canconduct fuel to the supplemental fuel inlet 334 and main fuel outlet 336(as opposed to the single integrated conduit or riser 338). The separateconduits or risers will typically run from a common fuel header.

Referring now specifically to FIG. 21, an alternative embodiment of theflare burner 330 is illustrated. This embodiment is the same as theembodiment of the burner 330 described above, except it also includes apre-mix chamber extension cylinder 400. The pre-mix chamber extensioncylinder 400 extends the length of the pre-mix chamber 332. In thisembodiment, the pre-mix chamber has a length (or height) to insidehydraulic diameter ratio in the range of from about 1:1 to about 4:1,more preferably in the range of from about 1:1 to about 3:1. Mostpreferably, in this embodiment, the pre-mix chamber has a length (orheight) to inside hydraulic diameter ratio of about 1.5:1. The cylinder400 comprises a top section 402, a bottom section 404 and a mid-section406 connecting the top section and bottom section together. Themid-section 406 is attached to the internal sidewall 367 of the annularfuel membrane 360.

Due to the pre-mix chamber extension cylinder 400, the top 342 andair/fuel outlet 350 of the pre-mix chamber 332 are spaced above the mainfuel outlet 336. The top 342 and air/fuel outlet 350 of the pre-mixchamber 332 are in the range of from about 0.5 inches to about 10inches, preferably in the range of from about 6 inches to about 8inches, above the main fuel outlet 336. The exact distance can varydepending on the type of fuel being flared, the particular application,the permitted height of the flame envelope and other factors. The bottom344 of the pre-mix chamber 332 is approximately flush with or about oneinch above the supplemental fuel inlet 334. As shown by FIG. 21, thepre-mix zone 331 in this particular embodiment (which includes theextension cylinder 400) includes a pre-mix space 331(a) below thepre-mix-chamber 332 (between the supplemental fuel injector 334 and thebottom 344 and air inlet 348 of the pre-mix chamber), the interior331(b) of the pre-mix chamber, and a pre-mix space 331(c) immediatelyabove the top 342 and air/fuel outlet 350 of the pre-mix chamber. Inthis embodiment, the predominant mixing of the air and fuel occurs inthe pre-mix chamber 332 (in the pre-mix zone 331(1 b)).

The top section 402 of the pre-mix chamber extension cylinder 400 servesboth as a wind shield as well as a physical barrier to delay ignition.Specifically, the top section 402 offsets the detrimental cross flow aireffects which can force the flame inside the diameter of the pre-mixchamber and interfere with the smokeless capacity of the flare burner.The top section 402 also functions to isolate the pre-mix fuel streamfrom the diffusion flame ignition. Similarly, the bottom section 404 ofthe cylinder 400 serves as a bottom wind shield and helps prevent theflame from being pulled back and causing premature ignition. Again, theincreased length of the pre-mix chamber 332 created by the extensioncylinder 400 enhances mixing of the fuel and air in the pre-mix chamber.The extension cylinder is not necessary in all applications; e.g., itmay not be necessary when cross-flow effects are not an issue or whenlow molecular weight fuels are being flared. The inclusion ornon-inclusion of the shield will depend on the molecular weight andheating value of the fuel to be flared, whether the fuel containssaturated or unsaturated hydrocarbons, the involved temperature andpressure and other factors.

In the embodiment shown by FIG. 21, the internal sidewall 367 of themembrane 360 is attached to the mid-section 406 of the extensioncylinder 400. In an alternate embodiment, as exemplified by FIGS. 25-28and explained below, the fuel membrane 360 can be spaced outwardly fromthe extension cylinder 400 (and hence the exterior surface of thepre-mix chamber 332) in order to provide a space between the exteriorsurface of the extension cylinder and the main fuel outlet 336. Thespace allows air to be entrained from below the burner to a pointadjacent to the fuel ports 374 disposed on an inner portion of the mainfuel outlet 336.

Referring to FIGS. 20 and 21, operation of the flare burner 330 will bedescribed. A portion of the fuel to be flared (generally depicted byblack arrows) is conducted through the main branch 380 of the fuel feedconduit 338 to the fuel membrane 360 and to the main fuel outlet 336. Aportion of the fuel to be flared is also conducted from through thesupplemental branch 390 of the fuel feed conduit 338 to the supplementalfuel inlet 334. The injection of fuel from the supplemental fuel inlet334 into the pre-mix zone 331 and pre-mix chamber 332 entrains air intothe pre-mix space 331(a) and through the air inlet 348 into the pre-mixchamber whereby a mixture (preferably a substantially homogenousmixture) of fuel and air is formed in the pre-mix zone and caused toexit the air/fuel outlet 350. The fuel and air continue to mix for ashort distance above the air/fuel outlet 350. The remaining fuel to beflared is injected from the main fuel outlet 336 around the perimeter368 of the air/fuel outlet 350 of the pre-mix chamber and hence aroundthe air/fuel mixture exiting the air/fuel outlet of the pre-mix chamber.Again, when the extension cylinder 400 is installed, additional mixingis gained and the pre-mix stream exiting the air/fuel outlet 350 isisolated from premature ignition by interaction with the diffusion flameformed upon discharge of the fuel from the main fuel outlet 336. Use ofthe extension cylinder 400 serves to enhance the overall effect createdby utilization of the pre-mix stream. The flare burner 330 is preferablydesigned and operated in a manner such that the amount of air entrainedinto the pre-mix zone 331 including the pre-mix chamber 332 is in excessof the stoichiometric amount of air required to combust the fuelinjected into the pre-mix zone. The excess air is imparted to the centerof the flame envelope for combustion of fuel therein. As explainedfurther below, however, in some applications the burner 330 is designedand operated in a manner such that the amount of air entrained into thepre-mix zone 331 including the pre-mix chamber 332 is equal to or lessthan the stoichiometric amount of air required to combust the fuelinjected into the pre-mix zone. The injection of a “fuel-rich” mixtureof fuel and air (i.e., a mixture having less than the stoichiometricamount of air required to support combustion of the fuel introduced intothe pre-mix zone) into the central portion of the flame envelope isdesirable in some applications.

The flare burner 330 achieves the same advantages that are achieved bythe flare burners 30, 130 and 230. The flame envelope 100 generallydepicted by FIG. 24 is also created by the flare burner 330.

Referring now to FIGS. 25-28, a modification that can be made to thefourth embodiment of the inventive flare burner described above (theembodiment shown by FIGS. 19-23) is illustrated. The same modificationcan be made to the first, second and third embodiments of the inventiveflare burner described above as well.

In this embodiment, the flare burner 330 includes the pre-mix chamberextension cylinder 400. However, instead of being attached directly tofuel membrane 360, the extension cylinder 400 (and hence the pre-mixchamber 332) is spaced inwardly from the fuel membrane to provide an airpathway between the extension cylinder and fuel membrane to allow air toeffectively reach the fuel ports 374 disposed on the inner portion ofthe main fuel outlet 336. The diameter of the extension cylinder 400(and hence the pre-mix chamber 332) is significantly smaller than theinside diameter of the fuel membrane 360. In this embodiment, thepre-mix chamber has a length (or height) to inside hydraulic diameterratio in the range of from about 0.5:1 to about 4:1, more preferably inthe range of from about 1:1 to about 3:1. Most preferably, the pre-mixchamber has a length (or height) to inside hydraulic diameter ratio inthe range of from about 1.5:1.

Due to the smaller diameter of the extension shield 400, an annularspace 430 exists between the internal sidewall 367 of the fuel membrane360 and the exterior surface of the extension cylinder 400 (which isalso the exterior surface 349 of the sidewall 346 of the pre-mix chamber332). A plurality of thin, rectangular gusset plates 432 are utilized tocenter and hold the extension cylinder 400 (and hence the pre-mixchamber 332) within the fuel membrane 360. As illustrated, four plates432 are disposed 90° apart within the annular space 430. One end of eachplate 432 is attached to the internal sidewall 367 of the fuel membrane360. The other end of each of the plates 432 is attached to the exteriorsurface of the extension cylinder 400 (which is also the exteriorsurface 349 of the sidewall 346 of the pre-mix chamber 332). Other thanthis above modification, the burner 330 illustrated by FIGS. 25-28 isthe same in all respects as the embodiment illustrated by FIGS. 19-23and described above.

The main fuel outlet 336 is still located in a position with respect tothe top 342 of the pre-mix chamber such that fuel can be injected fromthe main fuel outlet 336 around the perimeter 368 of the air/fuel outlet350 of the pre-mix chamber. The annular space 430 merely provides an airpathway between the extension cylinder and fuel membrane to allow freshoxidizer to effectively reach the fuel ports 374 disposed on the innerportion of the main fuel outlet 336. The operation of the burner 330remains the same, except fresh air is entrained from below the burner bythe motive force of the inner row of fuel ports 374 through the annularspace 430. The entrained air is in close proximity to the fuel beingdischarged by the inner row of fuel ports 374 on the main fuel outlet336 and mixes therewith. For example, the enhanced mixing regimenprovided by the annular space 430 is useful when relatively heavy andunsaturated fuel stocks, which tend to smoke more readily, are flared.It optimizes the burner for soot free combustion.

As will be understood by those skilled in the art, the same modificationcan also be made to the other three embodiments of the inventive flareburner described above. For example, in modifying the embodimentillustrated by FIGS. 4-8, the cross-sectional diameter of the pre-mixchamber 32 is reduced and the pre-mix chamber 32 is spaced inwardly fromthe fuel membrane 60. Either the internal sidewall 67 of the annularfuel membrane 60 or the sidewall 46 of the pre-mix chamber 32 is added(as shown, the internal sidewall of the membrane and the sidewall of thepre-mix chamber are the same). The annular seal 68 is eliminated.Spacing the pre-mix chamber 32 inwardly from the fuel membrane 60provides an air space between the pre-mix chamber and fuel membrane.Fresh air can then be entrained from below the burner to a point inclose proximity to the fuel that is discharged from the fuel ports 74 onthe inner portion of the main fuel outlet 36. The pre-mix chamber 32 canbe centered within and attached to the fuel membrane 60 with a pluralityof gussets as shown by FIGS. 25-28.

FIG. 28 generally depicts the flame envelope 100 created by the modifiedflare burner 330 illustrated by FIGS. 25-27 (as well as the burners 130,230 and 330 if modified in the same manner). As shown, excess air isinjected from the pre-mix chamber 332 into a center portion 102 of theflame envelope 100. The excess air, depicted by air pockets 103 in FIG.28 mixes with fuel in the center portion 102 of the flame envelope 100to form, in effect, two initial zones of flammability, zone 104(a) and104(b). Air is also entrained from below the burner 330 through theannular space 430 to a point in close proximity to the fuel beingdischarged by the inner row of fuel ports 374 on the main fuel outlet336. The air entrained through the annular space 430 enhances the mixingregimen and creates faster and more uniform combustion within theoverall flame envelope 100. As shown by FIG. 28, the flame envelope 100has a length 106 that is substantially less for the same amount of fuelthan the length 23 of the prior art flame envelope 20 shown by FIG. 3.

General Information

The partial pre-mix approach of the present invention allows two flamezones to be initiated within the same flame envelope as the fuel isflared. The outer flame zone is typical to what would normally beobserved with a burner of the type utilized heretofore, i.e., a typeutilizing only diffusion mixing. The outer layers of gas are shreddedaway to expose consecutive layers of gas for repeated diffusion andsubsequent combustion. The second flame zone is created by the pre-mixzone of the burner which delivers a combustible mixture to the inside ofthe main flame envelope. This combusting flow field serves to create anappreciable turbulent regime at the core of the flame which is atypicalof a normal diffusion flame. As the pre-mix zone becomes more fuel lean,the flame will become shorter due to the additional oxidizer deliveredto the core of the flame. The excess air is utilized by the remainingflame cloud and functions to shorten the flame (or allow the mass flowto be increased) while also serving further as a quench mechanism todiminish emissions such as nitrous oxides and carbon monoxide. Theexcess air also reduces the formation of soot and results in thecombustion of any unburned hydrocarbons.

Each of the flare burners 30, 130, 230 and 330 is preferably designedand operated such that the amount of air entrained into the pre-mix zoneand injected into the central portion of the flame envelope is in therange of from about 15% to about 300% of the stoichiometric amount ofair required to support combustion of the fuel introduced into thepre-mix zone. Thus, both a fuel-rich approach (the injection of amixture of fuel and air having less than 100% of the stoichiometricamount of air required to support combustion of the fuel introduced intothe pre-mix zone into the central portion of the flame envelope) and afuel-lean approach (the injection of a mixture of fuel and air havingmore than 100% of the stoichiometric amount of air required to supportcombustion of the fuel introduced into the pre-mix zone into the centralportion of the flame envelope) can be utilized. Each approach has itsown advantages as compared to the typical diffusion/free jet drivencombustion regimen utilized heretofore. The particular approach utilizedwill depend upon the particular application including the type of fuelto be flared and the available pressure. The approach can be modified bytypical porting and fuel delivery mechanisms.

When a fuel rich approach is utilized, the fraction of fuel injectedinto the center of the flame envelope will initiate a smaller envelopeof combustion at the core of the flame which will serve to shorten theflame while also creating an additional turbulent combustion zone at thecenter of the flame envelope. When a fuel-lean approach is utilized, theflame envelope will be shortened appreciably due to the larger pre-mixedfuel fraction combusting at the core of the flame. The excess aircarried by the pre-mix flow regimen then serves to further initiatecombustion relative to the center of the remaining flame envelope. Theadditional turbulence created by the fuel expanding at the center of theflame during combustion then serves to increase the mixing regimen forthe remaining fuel by fracturing the dense fuel core and pushing it tothe outer flame boundary.

When a fuel-rich approach is utilized, it is important for the pre-mixstream delivered to the center of the flame envelope to remain withinthe range of combustibility. If not, the augmented mixing and combustionin the center of the flame envelope may not occur. The enhanced mixingis benefited by a pre-mixed flame which initiates at the core of theflame and expands at an appreciable velocity to create significantturbulence at the core of the flame.

In most applications, however, injection of a “lean” mixture of fuel andair (i.e., a mixture having more than 100% of the stoichiometric amountof air required to support combustion of the fuel introduced into thepre-mix zone) into the central portion of the flame envelope is desired.In most applications, the amount of air entrained into the pre-mix zoneand injected into the central portion of the flame envelope is in therange of from about 125% to about 300% of the stoichiometric amount ofair required to support combustion of the fuel introduced into thepre-mix zone. Preferably, the amount of air entrained into the pre-mixzone is in the range of from about 150% to about 300%, more preferablyfrom about 175% to about 300%, of the stoichiometric amount of airrequired to support combustion of the fuel injected into the pre-mixzone. As the amount of excess air entrained into the pre-mix zoneincreases (that is, as the amount of air entrained into the pre-mix zonein excess of the stoichiometric amount of air required to supportcombustion of the fuel introduced into the pre-mix zone increases), thebenefit with respect to flame length and emissions also increases.Although an amount of air entrained into the pre-mix zone greater than300% of the stoichiometric amount of air required to support combustionof the fuel injected into the pre-mix zone would be advantageous, itwould require an extraneous source of air entrainment (such as steaminjection) and possibly other modifications, and may therefore be costprohibitive.

The amount of air entrained into the pre-mix zones of each of theburners 30, 130, 230 and 330 is highly dependent on the pressure andmass flow of the fuel injected from the supplemental fuel inlet, thetype of fuel being flared, the structure of the supplemental fuel inletincluding the number and size of the ports therein, the placement of thesupplemental fuel inlet with respect to the air inlet into the pre-mixchamber and the size of the air inlet. In most applications, theultimate goal is to achieve a highly dilute, preferably inflammablemixture of fuel and air. An inflammable, lean mixture will quicklyassimilate the fuel required to become again combustible once inside thecore of the flame envelope. Once a flammable mixture is achieved, theair and gas will then create a large flame zone on the inside of theflame envelope which will significantly increase the rate at which thefuel is oxidized while also creating significant turbulence to augmentthe diffusion mixing on the external surface of the flame zone as well.The additional mass transported to the center of the flame envelope alsoserves as a quench mechanism to lower the production of emissions suchas nitrous oxides and carbon monoxide. The added rate at whichcombustion occurs while maintaining two flame fronts also serves tolower the production of carbon monoxide and soot, and further reducesthe release of unburned hydrocarbons.

The fuel is injected into the pre-mix zone with sufficient momentum toentrain air radially and from below the burner into the jet(s) of fueland pre-mix zone. Depending upon the molecular weight of the fuel andthe delivery pressure available for entrainment, the burner can entrainair from up to 2 feet below the supplemental fuel inlet.

Preferably, the amount of fuel introduced into the pre-mix zone of eachof the burners 30, 130, 230 and 330 is in the range of from about 5% toabout 50%, more preferably in the range of from about 10% to about 30%,of the total amount of fuel to be flared by the flare burner. Mostpreferably, the amount of fuel introduced into the pre-mix chamber is inthe range of from about 10% to about 25% of the total amount of fuel tobe flared by the flare burner. The amount of fuel introduced into thepre-mix zone can be controlled by manipulating the diameter of the fuelports and the pressure of the fuel.

The greater the percentage of fuel introduced into the pre-mix zone, theshorter the flame and the greater the smokeless capacity of the burner.However, a proper balance between the percentage of fuel injected intothe pre-mix zone and the amount of air that can be entrained into thepre-mix zone must be achieved. When a fuel-lean approach is utilized, itis usually important for the amount of air entrained into the pre-mixzone to be at least about 125% of the stoichiometric amount of airrequired to support combustion of the fuel injected into the pre-mixzone. A lesser amount of air could create a very reactive (combustible)mixture that could make the burner prone to either burn-back orflashback at maximum rates, eventually causing damage to the burner. Thegreater the amount of entrained air the greater the quench effect andthe lower the flame speed of the fuel. This condition is ideal foraugmenting the delay in ignition of the pre-mix stream in order toensure that the ignition point of the pre-mix stream is local to thecore of the flame prior to combustion for maximum benefit.

A sufficiently dilute stream of air and fuel will assure that themixture of air and fuel is not ignited until the mixture exits theair/fuel outlet and reaches the center of the flame envelope. Once themixture of fuel and air exits the air/fuel outlet and enters the flameenvelope, the mixture then assimilates sufficient additional fuel toreach a combustible mixture at which time the fuel ignites inside themain flame envelope. This flow regimen creates a flame within a flame ora toroidal flame geometry combusting with two individual flame fronts.The additional turbulence created by the gas expanding at the center ofthe flame during combustion then serves to increase the mixing regimenfor the remaining fuel by fracturing the dense fuel core and pushing itto the outer flame boundary. This approach reduces the flame's heightand ability to smoke, while also increasing the overall combustionefficiency due to increased mixing.

It is important that the air/fuel mixture in the pre-mix zones of eachof the burners 30, 130, 230 and 330 does not combust until it exits theair/fuel outlet of the pre-mix zone. Combustion inside of the pre-mixchamber, for example, would back pressure the pre-mix chamber andgreatly reduce the amount of air entrained into the pre-mix chamber.

By delivering only a portion of the fuel to be flared to the pre-mixzones of each of the burners 30, 130, 230 and 330, the overallcross-sectional size of the burners is comparatively small. It would besize prohibitive to design and build a burner capable of supplying 100%of the air needed for combustion in a total pre-mix approach. Theventuri or mixer portion of such a burner would necessarily beappreciably large and lack the ability to accommodate low fuelpressures.

Although the pre-mix chamber of each of the inventive burners 30, 130,230 and 330 is relatively small, the set up is capable of providingsufficient air and fuel to create a pre-mixed air and fuel stream withan appreciable amount of entrained excess air. As a result, asignificant increase in the overall flow of fuel may be realized with anequivalent flame height and diameter. Depending on the type of fuel tobe flared, the inventive burners can easily accommodate a fuel flow ratethat can be designed to deliver fuel in excess of 1.4 times the ratetypically achievable by the diffusion jet-type burners utilizedheretofore. In most cases, this can also be accomplished whilemaintaining roughly the same flame length and diameter. If a largerflame height can be tolerated, a fuel flow rate that is appreciablyhigher in flow rate can be achieved as compared to the diffusionjet-type burners utilized heretofore. In addition, in connection witheach embodiment of the inventive burner, the ignition spacing and turndown capabilities can be conserved while the fuel flow rates areincreased. In connection with low molecular weight fuels, the radiantfraction of the flame may also be somewhat decreased with the temperingof the flame, reducing the overall flame temperature. In some cases,this allows the burners to maintain or only minimally increase thedistance between the burners and the fencing even though the fuel flowrate has been increased. The excess air delivered to the center of theflame serves not only to impart air to the center of the flame but alsoto decrease the timed rate in which the resulting fuel cloud is oxidizedupon exiting the tip of the burner. This results in a cleaner,smoke-free flame that is proportionally shorter for a given heatrelease. The dilution and subsequent quench effect to the flame alsoserves to decrease nitrous oxide and carbon monoxide emissions. The flowof fuel and air through the pre-mix chamber also aids in cooling theburner assembly.

Various configurations of the supplemental fuel inlet have beendescribed. Additional configurations are also possible, includingmulti-point injector bodies or headers drilled to maximize airentrainment and mixing in view of available fuel pressures. The lowersection of each of the embodiments described above can include a Coandasurface or can be a straight section. If Coanda surfaces are utilized,the ports in the supplemental fuel inlet can be round orifices (jets) orslots. In addition to Coanda technology, the fuel can be injected fromthe supplemental fuel inlet at a relatively high velocity to rapidlyachieve a mixture of fuel and air that can be injected into the centerof the flame envelope. The dimensions of the various components of theinventive flare burner including the dimensions of the pre-mix chamberand fuel membrane can vary. Further, a myriad of port configurations(for example, sizes of ports; spacing between ports) can be used inassociation with the main fuel outlet and the supplemental fuel inlet.The particular dimensions and configurations utilized will depend on thetype of fuel and the molecular weight, temperature, heating value andreactivity thereof, operational parameters (for example, the availablepressure) and other factors.

Although it is not generally necessary, a tertiary inerting fluid can beinjected into the pre-mix zone of the inventive flare burner (any of theembodiments of the flare burner) to enhance the entrainment of air intothe pre-mix zone. Examples of tertiary inerting fluids that can be usedinclude steam, air and nitrogen. Steam is preferred.

The drawings illustrate round and rectangular (polygonal) embodiments ofthe inventive flare burner. Each embodiment of the inventive flareburner can be formed in other geometries as well. For example, inaddition to round and rectangular shapes, elliptical, triangular,square, pentagonal, octagonal and other polygonal shapes can beemployed. These other geometric shapes may prove beneficial from a costor fabrication standpoint. The optimum approach is to create a diluteexcess air stream which can then be delivered from the pre-mix chamberto the center of the main body of the flame. A fuel rich stream,however, still offers benefits over the diffusion only type burnersutilized heretofore due to the enhanced mixing created by the inventiveburner.

The Inventive Ground Flare

Referring now to FIG. 29, the inventive ground flare is schematicallyillustrated and generally designated by the reference numeral 420. Theground flare 420 comprises a plurality of flare burners 422, anenclosure 424 extending around the flare burners and a fuel supply line426 for supplying fuel to the flare burners.

The flare burners are arranged in rows 430(a)-(f) and rows 432(a)-(e).Rows 430(a)-(f) form a first stage 434 of the flare burners 422, whereasthe rows 432(a)-(e) form a second stage 436 of the flare burners. Atleast one of the flare burners 422 is one of the embodiments of theinventive flare burner described above. Preferably, each of the flareburners 422 in the second stage 436 of flare burners 422 (the burnersutilized when a relatively high volume of fuel needs to be flared) isone of the embodiments of the inventive flare burner described above. Ifdesired, each of the flare burners 422 in both the first stage 434 ofburners and the second stage 436 of burners is one of the embodiments ofthe inventive flare burner described above.

The fuel supply line 426 comprises a main line 440 which terminates in adistribution manifold 442. A first stage supply line 444 and a secondstage supply line 446 are attached and in fluid communication with thedistribution manifold 442. Individual first stage supply lines450(a)-(f) run from the first stage fuel supply line 444 tocorresponding burner rows 430(a)-(f). Similarly, individual second stagesupply lines 452(a)-(e) run from the second stage fuel supply line 446to corresponding burner rows 432(a)-(e). For example, the first end 382of the main branch 380 of the fuel feed conduit 338 of the inventiveflare burner 330 is attached to one of the individual supply lines450(a)-(f) or 452(a)-(e). If another type of flare burner is alsoutilized in the ground flare 420, the fuel feed conduit of such burneris attached as appropriate to one of the individual supply lines450(a)-(f) or 452(a)-(e).

A series of pilots 460(a)-(f) are in fluid communication with the firststage supply line 444 and positioned with the appropriate burner andfuel separation prior to ignition. Pilots are typically located adjacentto the first flare burner 422 in corresponding rows 430(a)-(f).Similarly, a series of pilots 462(a)-(e) are in fluid communication withthe second stage supply line 446 and positioned adjacent to the firstflare burner 422 in corresponding rows 432(a)-(e).

The enclosure 424 surrounds the flare burners 422 and comprises aplurality of posts 470 and fence sections 472 connected between theposts. The enclosure or fence is in the range of from about 30 feet toabout 60 feet high. The enclosure 424 is designed such that air can bepulled into the ground flare through and under the enclosure.

In operation of the inventive ground flare 420, fuel to be flared isconducted through the main line 440 to the distribution manifold 442. Avalve control system (not shown) functions to distribute the fuel toeither the first stage fuel supply line 444 or both the first stage fuelsupply line 444 and the second stage fuel supply line 446. If arelatively low volume of fuel is conducted to the distribution manifold442, the valve system directs the fuel only to the first stage fuelsupply line 444. If the volume of fuel gas conducted to the distributionmanifold 442 is relatively high, the fuel is conducted to both the firststage fuel supply line 444 and the second stage fuel supply line 446.Additional staging can also be incorporated to cycle in and out asneeded. Fuel is conducted from one or both of the fuel supply lines 444and 446, depending on the volume of the fuel, to the correspondingindividual supply lines 450(a)-(f) and/or 452(a)-(e). The fuel isconducted from the individual supply lines 450(a)-(f) and/or 452(a)-(e)to the flare burners 422 in the corresponding rows 430(a)-(f) and432(a)-(e).

As necessary, the pilots 460(a)-(f) and 460(a)-(e) ignite the fueldischarged from the corresponding first burner 422 in each of the row.The ignited fuel from the first burner 422 in each row then ignites thefuel being discharged from the adjacent burner which in turn ignites thefuel being discharged from the next burner in the row and so on untilthe fuel being discharged from each of the burners in the row has beenignited. The air required for combustion is pulled through and/or underthe walls of the enclosure 424. It is not necessary to separately supplyair to the burners 422 or ground flare.

The inventive ground flare can be used to combust from a relativelysmall volume of fuel (for example, 3,000 pounds per hour or less) to avery large volume of fuel gas (for example, 10,000 to 15,000 pounds perhour and up depending on the molecular weight of the fuel to be flared,pressure availability, temperature and other factors). Even at a veryhigh flow rate (for example, 10,000 pounds per hour), the flame envelopecreated by the inventive ground flare burner can be contained in atypical ground flare enclosure. Due to the structure of the inventiveflare burner, a higher volume of fuel can be flared with smaller portsand higher pressures without significantly increasing the height of theflame envelopes created by the ground flare. Alternatively, the flameheights can be decreased allowing the enclosure 424 to be reduced inheight. The inventive burners pump air from below the burners whichallows the burners to be placed closer to the ground, again resulting ina reduction in the required height of the enclosure 424. A smallerportion of land may be required due to a smaller number of burners andrelated components.

In many cases, existing ground flares can be retrofitted with theinventive flare burner 422 to allow more fuel to be flared withoutcausing the height of the flame envelope to significantly exceed theheight of the enclosure surrounding the ground flare. Also, due to thestructure of the burner, the smokeless rate for a given flare tip may besignificantly larger in range. With a realized increase in throughput,more gas can be delivered per an individual header. This can result infewer headers coupled with fewer control mechanisms such as gas controlvalves, shut-off valves, regulators and physical piping. Increasedcapacity with fewer headers also allows for a smaller enclosure 434.

The inventive ground flare can be used to flare various types of fuelgas. Examples include saturated and unsaturated hydrocarbons such aspropane and propylene and mixtures thereof, alone or with hydrogen,water vapor and/or inert gases such as nitrogen, carbon monoxide, argon,etc.

The above description of the inventive ground flare is intended toillustrate the ground flare and particularly how the inventive flareburner is used in association therewith. As understood by those skilledin the art, ground flare installations can vary widely in terms of howthey are configured, the number and types of burners, headers, flowsystems, control valves and related components, the type and height ofthe enclosure surrounding the installation and in many other ways. Theinventive ground flare encompasses any ground flare installation inwhich the inventive flare burner is utilized.

The Inventive Method

In accordance with the inventive method, fuel is burned in one of theinventive flare burners 30, 130, 230, or 330. Referring to FIG. 24, thefuel is injected through a fuel injector body (i.e., the main fueloutlet 36, 136, 236 or 336) into the combustion zone 101 and ignited tocreate a flame envelope 100 and combust the fuel. A portion of the fuelto be burned is introduced into the pre-mix zone including the pre-mixchamber of the burner (i.e., the pre-mix chamber 32, 132, 232 or 332) ina manner that entrains air into the pre-mix zone and creates a mixture(preferably a substantially homogenous mixture) of air and fuel withinthe pre-mix zone. The mixture of air and fuel is then injected from thepre-mix chamber into a central portion 104 of the flame envelope. Again,as discussed above, the amount of air entrained into the pre-mix zoneand injected into the central portion of the flame envelope can rangefrom a fuel rich but combustible mixture to a mixture having entrainedair in excess of the stoichiometric amount required for combustion. Thispre-mixed fuel and air stream injected into the center of the flameenvelope initiates a second flame zone, creating a toroidal shaped flameenvelope. The overall result is faster and more uniform combustion ofthe overall flame envelope thereby achieving the advantages discussedabove in connection with the inventive flare burner.

As discussed above, the amount of air entrained into the pre-mix zoneand injected into the central portion of the flame envelope ispreferably at least about 15% of the stoichiometric amount of airrequired to support combustion of the fuel introduced into the pre-mixzone. In some applications, injection of a “fuel-rich” mixture of fueland air (i.e., a mixture having less than 100% of the stoichiometricamount of air required to support combustion of the fuel introduced intothe pre-mix zone) into the central portion of the flame envelope issuitable. In most applications, however, injection of a “lean” mixtureof fuel and air (i.e., a mixture having more than 100% of thestoichiometric amount of air required to support combustion of the fuelintroduced into the pre-mix zone) into the central portion of the flameenvelope is desired. In most applications, the amount of air entrainedinto the pre-mix zone and injected into the central portion of the flameenvelope is in the range of from about 125% to about 300% of thestoichiometric amount of air required to support combustion of the fuelintroduced into the pre-mix zone.

The amount of fuel introduced into the pre-mix zone and pre-mix chamber(i.e., the pre-mix chamber 32, 132, 232 or 332) is in the range of fromabout 5% to about 50%, more preferably from about 10% to about 30%, mostpreferably from about 10% to about 25%, of the total amount of fuel tobe flared by the flare burner.

In order to further illustrate the invention, the following examples aregiven.

EXAMPLE 1

The first embodiment of the inventive flare burner, flare burner 30, wascompared to a prior art high capacity diffusion-type ground flareburner, namely the burner illustrated in FIGS. 1 and 2. Two of theinventive flare burners were tested, one approximately 30 inches inlength and the other approximately 16 inches in length. The inventiveflare burners were ported to match the three square inches of flow areacontained in the prior art flare burner.

The inventive flare burners were first tested singularly. Tests werecarried out using propane and propylene. Approximately 20% of the fuelwas injected into the pre-mix chamber of each of the inventive flareburners. The remaining fuel was then injected around the perimeter ofthe air/fuel mixture discharged from the pre-mix chamber. It wasdetermined that with both types of fuels, each of the inventive flareburners were able to support a significant flow of fuel while developinga smokeless flame. The flame envelope from each burner was found to bevery stable, capable of significant turndown ratios, and also verysymmetrical throughout the range of heat releases fired. The flameenvelopes from each burner were observed as being very short in lengthand having a small diameter.

The inventive flare burner having a length of approximately 30 incheswas then compared to the prior art burner. The two flare burners weretested side by side. The burners were attached to the same header toinsure that the same volume of fuel was supplied to each burner.

It was observed that the inventive flare burner produced a shorter flameenvelope in most of the test points observed. The inventive flare burnerremained lit at lower pressures during turn down, indicating a somewhatexpanded range of operability. At maximum fuel flow rates, the flameenvelope generated by the inventive flare burner was shorter in overalllength as compared to the prior art high capacity diffusion-type groundflare burner. In this scenario, however, the vertical cross-section(width) of the flame envelope created by the prior art flare burner waslarger than the flame envelope created by the inventive flare burner. Noburn-back was observed with the inventive flare burner until thepressure was notably under 1 psig. Radiation from the flame envelopegenerated by the inventive flare burner appeared to be equivalent to orslightly less than the radiation generated by the flame envelopeproduced by the prior art flare burner. During turn down conditions, theprior art flare burner smoked at approximately the same rate as theinventive flare burner. Trailing smoke typically could be noted fromboth burners at about the same flow rate and pressure. However, theinventive flare burner appeared to maintain a less dense trail of smokeat lower pressures than the diffusion type burner tip during initialtesting. The prior art burner transitioned to heavier smoke productionas pressure was reduced.

EXAMPLE II

The third embodiment of the inventive flare burner, flare burner 230,was also tested and compared to the prior art flare burner discussedabove. The performance of this embodiment of the inventive flare burnerappeared to be at least equivalent to the prior art burner. However, theinventive burner produced more smoke at low pressure than the firstembodiment of the inventive flare burner described in Example I. Therange of smokeless operation was comparative to the smokelessperformance of the prior art flare burner.

In this test, the corners of the pre-mix chamber of the inventive flareburner created complex flow patterns which visually appeared to inhibitthe mixing regimen in the pre-mix chamber to some extent. As a result,spurious stratified fuel rich zones were observed to form at the cornersof the pre-mix discharge area, resulting in visible smoke strataobserved throughout the surface of the flame zone. On the other hand,the inventive flare burner tested was able to handle almost three timesthe amount of fuel that could be handled by the prior art flare burner.

A weld used in assembling the test unit of the inventive flare burnerdescribed in this example was faulty and ultimately failed (only afterappreciable testing was carried out). The weld in question was utilizedonly for the test unit (which was made out of carbon steel); the failureof the weld was not due to a design issue and has no relevance to theoperation or performance of the actual burner. In any event, the testsshowed that the flare burner 230 is very capable of handling large fuelflows with minor smoke issues.

Thus, the present invention is well adapted to carry out the objects andattain the ends and advantages mentioned as well as those which areinherent therein. While numerous changes may be made by those skilled inthe art, such changes are encompassed within the spirit of thisinvention as defined by the appended claims.

1. A flare burner, comprising: a pre-mix zone including a pre-mixchamber, said pre-mix chamber having a top, a bottom, a sidewallconnecting said top to said bottom, an air inlet disposed in one of saidbottom and said sidewall and an air/fuel outlet disposed in said top; asupplemental fuel inlet for injecting fuel into said pre-mix zone, saidsupplemental fuel inlet being located in a position with respect to saidpre-mix zone such that the injection of fuel from said supplemental fuelinlet into said pre-mix zone entrains air into said pre-mix zone wherebya mixture of fuel and air is formed in said pre-mix zone and caused toexit said air/fuel outlet of said pre-mix chamber; and a main fueloutlet located in a position with respect to said top of said pre-mixchamber such that fuel can be injected from said main fuel outlet aroundthe perimeter of said air/fuel outlet of said pre-mix chamber.
 2. Theflare burner of claim 1 wherein said air inlet is disposed in saidbottom of said pre-mix chamber.
 3. The flare burner of claim 1 whereinsaid main fuel outlet is spaced outwardly from said pre-mix chamber toprovide an air entrainment space therebetween.
 4. The flare burner ofclaim 1 further comprising a fuel membrane disposed around the outsideperimeter of said pre-mix chamber, said membrane including a fuel inletand being in fluid communication with said main fuel outlet.
 5. Theflare burner of claim 4 wherein said fuel membrane and said main fueloutlet are spaced outwardly from said pre-mix chamber to provide an airentrainment space therebetween.
 6. The flare burner of claim 4 whereinsaid membrane is also in fluid communication with said supplemental fuelinlet.
 7. The flare burner of claim 1 further comprising a fuel feedconduit in fluid communication with said supplemental fuel inlet andsaid main fuel outlet for conducting fuel to said supplemental fuelinlet and said main fuel outlet.
 8. The flare burner of claim 1 whereinsaid main fuel outlet comprises a plurality of fuel ports disposedaround the perimeter of said air/fuel outlet of said pre-mix chamber. 9.The flare burner of claim 4 wherein said pre-mix chamber, including saidair/fuel outlet, and said fuel membrane and said main fuel outlet eachhave a round cross-section such that fuel can be injected annularly fromsaid main fuel outlet around the perimeter of said air/fuel outlet. 10.The flare burner of claim 1 wherein said sidewall of said pre-mixchamber includes an interior surface and an exterior surface, saidinterior surface having a section that is a Coanda surface.
 11. Theflare burner of claim 10 wherein said supplemental fuel inlet is locatedin a position with respect to said pre-mix chamber such that fuel can beinjected from said supplemental fuel inlet onto said Coanda surface. 12.The flare burner of claim 4 wherein said sidewall of said pre-mixchamber includes an interior surface and an exterior surface, saidinterior surface having a section that is a Coanda surface.
 13. Theflare burner of claim 12 wherein: said air inlet is disposed in saidbottom of said pre-mix chamber and said pre-mix chamber, including saidair inlet, and said membrane and said supplemental fuel inlet each havea round cross-section; and said Coanda surface annularly extends aroundsaid interior surface of said sidewall of said pre-mix chamber.
 14. Theflare burner of claim 13 wherein said supplemental fuel inlet is locatedin a position with respect to said pre-mix chamber such that fuel can beannularly injected from said supplement fuel inlet onto said Coandasurface.
 15. The flare burner of claim 10 wherein said interior surfaceincludes two opposing sections that are Coanda surfaces, and saidsupplemental fuel inlet is in a position with respect to said pre-mixchamber such that fuel can be injected from said supplement fuel inletonto each of said Coanda surfaces.
 16. The flare burner of claim 1wherein said pre-mix chamber has a length to inside hydraulic diameterratio in the range of from about 0.25:1 to about 4:1.
 17. The flareburner of claim 1 wherein said pre-mix chamber has a length to insidehydraulic diameter ratio of about 1:1 or less.
 18. A flare burner,comprising: a pre-mix zone including a pre-mix chamber, said pre-mixchamber having a top, a bottom, a sidewall connecting said top to saidbottom, an air inlet disposed in said bottom, an air/fuel outletdisposed in said top and a length to inside hydraulic diameter ratio inthe range of from about 0.25:1 to about 4:1; a supplemental fuel inletfor injecting fuel into said pre-mix zone, said supplemental fuel inletbeing located in a position with respect to said pre-mix zone such thatthe injection of fuel from said supplemental fuel inlet into saidpre-mix zone entrains air into said pre-mix zone whereby a mixture offuel gas and air is formed in said pre-mix zone and caused to exit saidair/fuel outlet of said pre-mix chamber; a main fuel outlet located in aposition with respect to said top of said pre-mix chamber such that fuelcan be injected from said main fuel outlet around the perimeter of saidair/fuel outlet of said pre-mix chamber; and a fuel feed conduit influid communication with said supplemental fuel inlet and said main fueloutlet for conducting fuel to said supplemental fuel inlet and said mainfuel outlet.
 19. The flare burner of claim 18 wherein said pre-mixchamber, including said air inlet and said air/fuel outlet, and saidmain fuel outlet have round cross-sections.
 20. The flare burner ofclaim 18 wherein said main fuel outlet is spaced outwardly from saidpre-mix chamber to provide an air entrainment space therebetween. 21.The flare burner of claim 19 further comprising an annular fuel membranedisposed around the outside perimeter of said pre-mix chamber, saidmembrane being in fluid communication with said main fuel outlet andhaving a top, a bottom and a sidewall connecting said top to saidbottom.
 22. The flare burner of claim 21 wherein said main fuel outletis attached to said top of said fuel membrane and comprises a pluralityof fuel ports extending around the perimeter of said air/fuel outlet ofsaid pre-mix chamber.
 23. The flare burner of claim 22 wherein said fuelmembrane and said main fuel outlet are spaced outwardly from saidpre-mix chamber to provide an air entrainment space therebetween. 24.The flare burner of claim 18 wherein said pre-mix chamber has a lengthto inside hydraulic diameter ratio of about 1:1 or less.
 25. The flareburner of claim 24 wherein said supplemental fuel inlet is spaced belowsaid air inlet of said pre-mix chamber.
 26. The flare burner of claim 18wherein said air/fuel outlet of said pre-mix chamber is spaced abovesaid main fuel outlet.
 27. A ground flare comprising a plurality offlare burners, an enclosure extending around the flare burners and afuel supply line for supplying fuel to the flare burners, wherein atleast one of the flare burners includes: a pre-mix zone including apre-mix chamber having a top, a bottom, a sidewall connecting said topto said bottom, an air inlet disposed in one of said bottom and saidsidewall and an air/fuel outlet disposed in said top; a supplementalfuel inlet for injecting fuel into said pre-mix zone, said supplementalfuel inlet being located in a position with respect to said pre-mix zonesuch that the injection of fuel from said supplemental fuel inlet intosaid pre-mix zone entrains air into said pre-mix zone whereby a mixtureof fuel gas and air is formed in said pre-mix zone and caused to exitsaid air/fuel outlet of said pre-mix chamber; and a main fuel outletlocated in a position with respect to said top of said pre-mix chambersuch that fuel can be injected from said main fuel outlet around theperimeter of said air/fuel outlet of said pre-mix chamber.
 28. Theground flare of claim 27 wherein said air inlet is disposed in saidbottom of said pre-mix chamber.
 29. The ground flare of claim 27 whereinsaid main fuel outlet is spaced outwardly from said pre-mix chamber toprovide an air entrainment space therebetween.
 30. The ground flare ofclaim 27 wherein said flare burner further comprises a fuel membranedisposed around the outside perimeter of said pre-mix chamber, saidmembrane including a fuel inlet and being in fluid communication withsaid main fuel outlet.
 31. The ground flare of claim 30 wherein saidfuel membrane and said main fuel outlet are spaced outwardly from saidpre-mix chamber to provide an air entrainment space therebetween. 32.The ground flare of claim 30 wherein said membrane is also in fluidcommunication with said supplemental fuel inlet.
 33. The ground flare ofclaim 27 further comprising a fuel feed conduit in fluid communicationwith said supplemental fuel inlet and said main fuel outlet forconducting fuel to said supplemental fuel inlet and said main fueloutlet.
 34. The ground flare of claim 27 wherein said main fuel outletcomprises a plurality of fuel ports disposed around the perimeter ofsaid air/fuel outlet of said pre-mix chamber.
 35. The ground flare ofclaim 30, wherein said pre-mix chamber, including said air/fuel outlet,and said fuel membrane and said main fuel outlet each have a roundcross-section whereby fuel can be annularly injected from said main fueloutlet around the perimeter of said air/fuel outlet.
 36. The groundflare of claim 27 wherein said sidewall of said pre-mix chamber includesan interior surface and an exterior surface, and said interior surfacehaving a section that is a Coanda surface.
 37. The ground flare of claim36 wherein said supplemental fuel outlet is located in a position withrespect to said pre-mix chamber such that fuel can be injected from saidsupplemental fuel outlet onto said Coanda surface.
 38. The ground flareof claim 30 wherein said sidewall of said pre-mix chamber includes aninterior surface and an exterior surface, said interior surface having asection that is a Coanda surface.
 39. The ground flare of claim 38wherein: said air inlet is disposed in said bottom of said pre-mixchamber and said pre-mix chamber, including said air inlet, and saidfuel membrane and said supplemental fuel inlet each have a roundcross-section; and said Coanda surface annularly extends around saidinterior surface of said sidewall of said pre-mix chamber.
 40. Theground flare burner of claim 39 wherein said supplemental fuel inlet isin a position with respect to said pre-mix chamber such that fuel can beannularly injected from said supplemental fuel inlet onto said Coandasurface.
 41. The ground flare burner of claim 36 wherein said interiorsurface includes two opposing sections that are Coanda surfaces, andsaid supplemental fuel inlet is in a position with respect to saidpre-mix chamber such that fuel can be injected from said supplement fuelinlet onto each of said Coanda surfaces.
 42. In a method of flaring fuelwith a flare burner wherein fuel to be flared is injected through a fueloutlet of the burner into a combustion zone and ignited to create aflame envelope and combust the fuel, the improvement comprising:introducing a portion of the fuel to be burned into a pre-mix zone ofsaid burner in a manner that entrains air into said pre-mix zone andcreates a mixture of air and fuel within said pre-mix zone; andinjecting said mixture of air and fuel from said pre-mix zone into acentral portion of said flame envelope.
 43. The method of claim 42wherein the amount of air entrained into said pre-mix zone and injectedinto said central portion of said flame envelope is in the range of fromabout 125% to about 300% of the stoichiometric amount of air required tosupport combustion of the fuel introduced into said pre-mix zone. 44.The method of claim 43 wherein the amount of air entrained into saidpre-mix zone and injected into said central portion of said flameenvelope is in the range of from about 150% to about 300% of thestoichiometric amount of air required to support combustion of the fuelintroduced into said pre-mix zone.
 45. The method of claim 42 whereinthe amount of the fuel introduced into said pre-mix zone is in the rangeof from about 5% to about
 50. % of the total amount of fuel to be flaredby said flare burner.
 46. The method of claim 45 wherein the amount ofthe fuel introduced into said pre-mix zone is in the range of from about10% to about 30% of the total amount of fuel to be flared by said flareburner.